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1.
Radioligand binding studies and functional assays on isolated smooth muscle preparations were performed in order to obtain a biochemical and functional characterization of the beta-adrenoceptor (beta-AR) subtypes involved in regulation of the smooth muscle relaxation of the calf's common digital artery. The results indicate that the common digital artery possesses two beta-AR populations (40% beta(1) and 60% beta(2)) and the beta(2)-subtype appears to predominate as far as function is concerned. Only the beta(2)-AR agonists clenbuterol and fenoterol caused dose-related relaxant effects, antagonized by propranolol, when tested in preparations precontracted both with PGF(2alpha) (1.4 x 10(-5) m) and noradrenaline (1.2 x 10(-6) m). In noradrenaline precontracted preparations the beta(1)-AR selective agonists dobutamine and xamoterol caused vasodilation which was not antagonized by (+/-)propranolol. While the functional relaxant effects of dobutamine may be attributed to its potent competitive alpha-AR blocking activity, further investigations are required to explain the effect of xamoterol. The vasodilator effect of (+/-)isoproterenol was irregular. The recorded contractile effects, mainly at dosages greater than 10(-6) m, suggest the loss of drug selectivity for beta-AR and alpha-AR activation. Indirect evidence indicates that the alpha-adrenoceptor (alpha-AR) population in this tissue which produces a strong contraction is functionally dominant over the beta-AR, suggesting limited therapeutic benefit for beta-AR drugs to control blood flow disorders in the calf's distal limb.  相似文献   

2.
OBJECTIVE: To determine the concentration and binding characteristics of alpha-adrenoceptor subtypes in smooth muscle cell membranes of equine ileum. SAMPLE POPULATION: Segments of longitudinal and circular smooth muscle from the ileum of 8 male and 8 female adult horses. PROCEDURE: Distribution of alpha-adrenoceptor subtypes was assessed by use of radioligand binding assays incorporating [3H]-prazosin and [3H]-rauwolscine, highly selective alpha1- and alpha2-adrenoceptor antagonists, respectively. Characterization of adrenoceptor subtypes was performed by use of binding inhibition assays. RESULTS: On the basis of binding affinity for specific radioligands, low- and high-affinity alpha1- and alpha2-adrenoceptors were detected. Concentration of low-affinity alpha2-adrenoceptors was significantly greater in male horses, compared with females. Competition studies confirmed the specificity of the radioligands used in the binding assays. Alpha1-adrenoceptors of both subtypes in male and female horses had a higher affinity for prazosin than phentolamine, whereas yohimbine did not compete with the radioligand for binding. For alpha2-adrenoceptors regardless of subtype, potency of inhibition elicited by each drug varied between sexes. In males, yohimbine was a more potent inhibitor than phentolamine, which was more potent than prazosin. In females, yohimbine was more potent than prazosin, which was more potent than phentolamine. CONCLUSIONS AND CLINICAL RELEVANCE: High- and low-affinity alpha1- and alpha2-adrenoceptors were detected in smooth muscle of equine ileum. Because alpha-adrenoceptor subtypes, particularly alpha2-adrenoceptors, are involved in the regulation of gastrointestinal tract function, characterization of these receptors may represent the basis for development of new therapeutic strategies for the control of gastrointestinal disturbances in horses.  相似文献   

3.
Beta-adrenoceptors are important regulators of cardiac function and their characteristics are known to change in human and canine diseased myocardium. This study aimed to determine the density and subtypes of beta-adrenoceptors in the normal and failing equine ventricular myocardium. Membrane preparations of the left papillary muscles were incubated with increasing concentrations of the nonselective beta-adrenoceptor antagonist [3H]-CGP12177. Saturable and reversible binding of [3H]-CGP12177 to myocardial membranes was demonstrated with Kd values (+/- s.d.) of 0.49 +/- 0.40 and 0.43 +/- 0.22 nmol/l and Bmax values of 93.4 +/- 20.5 and 110.0 +/- 21.2 and fmol/mg protein for normal (n = 19) and heart failure (n = 10) tissues, respectively. Heart failure had no significant effect on the density of ventricular beta-adrenoceptors. The cardiac beta-adrenoceptors were further characterised by studying displacement of [3H]-CGP12177 (0.6 nmol/l) with the beta1-selective antagonists CGP20712A and the beta2-selective antagonist ICI118.551. In normal ventricular muscle, CGP20712A was 26 times more potent than ICI118.551 (Ki values 30.4 +/- 24.8 and 814.1 +/- 485.2 nmol/l, respectively). In heart failure cases, CGP 20712A curves were monophasic with a Ki value of 45.6 +/- 39.7 nmol/l. ICI 118.551 curves were biphasic in 5 horses where 11-31% of the cardiac beta-adrenoceptors had a high affinity for ICI 118.551. These data suggest that the normal equine ventricular myocardium possesses predominately beta1-adrenoceptors, with no evidence for co-existence of a significant population of beta2-adrenoceptors. The density of beta-adrenoceptors did not appear to change in heart failure, but the appearance of receptors with a high affinity for ICI118.551 may suggest that, in some cases, heart failure increases the expression of beta2-adrenoceptors in equine ventricular myocardium. This study provides an insight into the role of the adrenergic system in heart disease in the horse. Further studies in this area are warranted.  相似文献   

4.
Palmar digital arteries and veins removed surgically from healthy horses under general anesthesia were cut into 4 mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for continuous measurement of vascular tension. In vitro vascular responses were determined for acetylcholine, acepromazine, isoxsuprine hydrochloride (isoxsuprine), prostaglandin E2 (PGE2), and prostaglandin I2 (prostacyclin). After preconstriction with norepinephrine hydrochloride (norepinephrine), or prostaglandin F2 alpha (PGF2 alpha), the concentrations needed to produce 50% maximum relaxation (EC50) and the maximum percentage of relaxation were determined for each drug.
Acetylcholine was the most potent arterial vasodilator (smallest EC50 value) and PGE2 was the least potent. Prostacyclin was the least potent venodilator (highest EC50 value); there were no differences between acetylcholine, acepromazine, isoxsuprine, and PGE2. Isoxsuprine produced greater arterial relaxation than all other agents. Isoxsuprine and acepromazine produced significantly greater venous relaxation than did acetylcholine and PGE2. Prostacyclin produced minimal vasodilation of arteries or veins. Acepromazine and isoxsuprine relaxed the veins significantly more than the arteries. When PGF2 alpha was used instead of norepinephrine to preconstrict the arteries and veins, the potency and effectiveness of acepromazine and isoxsuprine to produce vasodilation were significantly decreased. Results indicate that acepromazine and isoxsuprine can relax the equine digital vasculature but their effectiveness varies depending on the origin of the constriction.  相似文献   

5.
Vascular effects of ergovaline mediated by 5-hydroxytryptamine(HT)2A, 5-HT1B/1D, and alpha1 receptors were studied in isolated arterial preparations of rat and guinea pig. In rat tail artery ergovaline behaved as a potent contractile partial agonist showing an agonist potency (pEC50) of 8.86 +/- 0.03, a maximum response (Emax) of 59 +/- 2% with respect to 5-HT, and a partial agonist affinity (pK(P)) of 8.51 +/- 0.06. Ergovaline was equipotent with ergotamine (pEC50, 8.69 +/- 0.07; Emax, 52 +/- 4%; pK(P), 8.36 +/- 0.11). Contractile responses to ergovaline and ergotamine were surmountably antagonized by the 5-HT2A receptor antagonist ketanserin (3 nM). Antagonist affinity (apparent pA2) for ketanserin against ergovaline and ergotamine was 9.19 +/- 0.08 and 9.36 +/- 0.17, respectively. Ergovaline showed extremely slow on-set and off-set kinetics in rat tail artery. The construction of cumulative concentration-response curves required about 4 h, and the contractile response to ergovaline (30 nM), which completely abolished the subsequent contractile response to 5-HT (10 nM to 1 mM), could not be reversed by wash-out. In guinea pig iliac artery moderately precontracted with prostaglandin F2alpha (0.05 to 0.5 microM) ergovaline behaved as an agonist (pEC50, 7.71 +/- 0.10) with a potency similar to that of 5-HT (pEC50, 7.60 +/- 0.05). The contractile response to ergovaline was inhibited by the 5-HT1B/1D receptor antagonist GR127935 (10 nM). The apparent pA2 value for GR127935 against ergovaline was 8.90 +/- 0.12. Ergovaline (10 nM) produced no contractile response in guinea pig iliac artery when added before the PGF2alpha-induced precontraction but caused insurmountable blockade of the contractile response to the 5-HT1B/1D receptor agonist 5-carboxamidotryptamine (5-CT). The apparent pA2 value for ergovaline against 5-CT was 8.56 +/- 0.18. In rat thoracic aorta ergovaline (2 microM) activated alpha1 adrenoceptors only with low efficacy (Emax, 12 +/- 3%) but surmountably antagonized norepinephrine-induced contractions with a pK(P) of 7.07 +/- 0.12. It is concluded that the powerful constrictor effect of ergovaline mediated by activation of vascular 5-HT2A and 5-HT1B/1D receptors may explain the vascular symptoms of fescue toxicosis observed in livestock grazing tall fescue pastures infected with the endophytic fungus Neotyphodium coenophialum.  相似文献   

6.
Strips of bovine teat smooth muscle were studied. Their innervation was investigated with analytical pharmacology on field stimulated preparations. The content of noradrenaline in the teat wall and the sphincter region was determined. The main results were: teat smooth muscle has properties of single unit smooth muscle i.e. automaticity and active response to stretch. Especially the sphincter region is inclined to rapid phasic rhythmicity. The teat smooth muscle receives excitatory adrenergic innervation. The noradrenaline released from the nerves preferentially activates α-adrenoceptors, while β-adrenoceptors essentially are noninnervated and humoral. The sphincter region has a higher concentration of noradrenaline and a more intimate neuro-effector arrangement. This is probably of functional significance. Moderate chilling increases the response to adrenergic nerve stimulation while it is decreased at higher temperatures. This has most likely physiological importance. The results are discussed with respect to in vivo findings and it is concluded that the bovine teat smooth muscle with its excitatory adrenergic nerves forms a normally very efficient neuro-effector system with a particular strength in the sphincter around the streak canal.  相似文献   

7.
The effects of alpha- and beta-adrenoceptor agonists and antagonists were studied in the sheep ureterovesical junction. Non-specific adrenergic agonists such as adrenaline and noradrenaline induced contraction in the sheep ureterovesical junction, suggesting a predominance of alpha-over beta-adrenoceptors in this functional unity. An inhibition of the noradrenaline-induced contraction was observed after prior blocking with prazosin (10(-7) M) and yohimbine (10(-7) M), the effect of prazosin being more potent than that of yohimbine. The effect of phenylephrine on alpha 1-adrenoceptors was more potent than that of B-HT 920 on alpha 2-adrenoceptors. Isoproterenol caused a concentration-dependent relaxation that was inhibited by propranolol (10(-6) M), pafenolol (10(-5) M) and butoxamine (10(-5) M). These results suggest that ureterovesical junction contraction is mediated by both alpha 1 and alpha 2-adrenoceptors, alpha 1 predominating over alpha 2. Relaxation is mediated by beta-adrenoceptors of the beta 1 and beta 2 subtypes.  相似文献   

8.
We investigated the influence of the phase of the estrous cycle on mechanical responses elicited in sheep cervix by potassium chloride (KCl), acetylcholine chloride (ACh), prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E1 (PGE1). The cervix of adult ewes (n = 48) were classified according to the presence or absence of corpora lutea (luteal or follicular phase, respectively). Muscle strips of the circular and longitudinal layers were prepared in an organ bath and coupled to an isometric force transducer. Concentration-response curves were obtained noncumulatively. KCl and ACh produced concentration-dependent contractions in all preparations in both phases of the estrous cycle. However, maximum effect, EC50 and slope values of KCl and ACh were not significantly different between muscle layers, as well as between the phases of the estrous cycle. The prostanoid, PGF2 alpha, produced a significant reduction in the amplitude of spontaneous contractions for all preparations. The depressant effect of PGF2 alpha on spontaneous contractions of circular smooth muscle was significantly greater during the follicular than the luteal phase, whilst the depressant effect of PGF2 alpha on the longitudinal layer did not differ between phases of the estrous cycle. PGE1 significantly reduced the amplitude of spontaneous contractions on circular but not on longitudinal preparations. In conclusion, we have characterized with in vitro preparations of circular and longitudinal muscle layers of ewes during the follicular and luteal phases of the estrous cycle, the parameters of the K- and ACh-induced contractions on cervix and the efficacy of PGF2 alpha and PGE1 on inhibition spontaneous contractile activity.  相似文献   

9.
Heat-stable E. coli and V. cholerae enterotoxins and E. coli endotoxin were tested on the following smooth muscle preparation: vascular; rabbit aorta; rat mesenteric arterioles, and intestinal, rabbit jejunum; pig duodenum; dog jejunal lamina propria smooth muscle. The results indicated that in most preparations used, the prime action of heat-stable enterotoxin from pathogenic strains of E. coli consisted in neutralizing the effects of both alpha or beta adrenergic agonists. In this respect the effect of enterotoxin appeared similar to that of alpha or beta adrenergic blockers. Using the same models, it was found that this enterotoxin did not interfere with the effects of cholinergic agonists or of biogenic amines. Control heat-stable enterotoxin preparations and other tested substances proved inactive, suggesting that different receptor sites might exist for these agents in our models. It appears that smooth muscle preparations are well suited for bioassay of active heat-stable E. coli enterotoxin.  相似文献   

10.
Alpha-adrenoceptors mediate contractile responses in equine digital veins (EDVs) and arteries. Vascular smooth muscle alpha(1)-adrenoceptor subtypes have been implicated in a number of conditions, such as acute equine laminitis, and are therapeutic targets for the treatment of this condition. Digital veins, rather than arteries, were investigated in the present study because they have been specifically implicated in the pathophysiology of acute laminitis. The order of potency of a series of alpha(1)-adrenoceptor-selective agonists and antagonists was determined in isolated rings of EDVs under conditions of isometric tension. A61603 was the most potent agonist, with a higher potency (76-fold greater) than phenylephrine (PHE), suggesting the presence of the alpha(1A)-adrenoceptor subtype. Prazosin (30 nm) caused competitive inhibition of the responses to A61603 and PHE, with pK(b) values of 8.05 +/- 0.28 and 8.20 +/- 0.27, respectively. In addition, the alpha(1A)-adrenoceptor antagonist, WB4101 (10 nm), also caused competitive inhibition of the responses to the two agonists, with pK(b) values of 8.37 +/- 0.16 and 8.54 +/- 0.23, respectively, confirming the presence of the alpha(1A)-adrenoceptor subtype in EDVs. The selective alpha(1D)-adrenoceptor antagonist, BMY7378 (100 nm) did not cause a significant change in the response to the agonists, giving lower pK(b) values (6.97 +/- 0.27 and 6.88 +/- 0.17 vs. A61603 and PHE, respectively). Chloroethylclonidine dihydrochloride (45 microm, 30 min), used to produce selective inactivation of alpha(1B)-adrenoceptors, caused noncompetitive inhibition of the response to PHE, but was without effect on the response to A61603. These findings indicate that EDVs possess at least two different alpha(1)-adrenoceptor populations, which are predominantly of the alpha(1A) and alpha(1B) subtypes. These data may assist in the development of more selective antagonists for therapeutic use in horses.  相似文献   

11.
Rings of equine digital vein examined under conditions of isometric tension recording constricted to alpha-adrenoceptor agonists with an order of potency of 5-bromo-6-[2-imidazolin-2-yl-amino]-quinoxaline bitartrate (UK 14304) = noradrenaline > 6-Allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-(4,5-d) azepine (BHT-920) > phenylephrine > dopamine > methoxamine. The maximum force generated was greatest for the non-selective agonist noradrenaline and lowest for the alpha2-selective agonist BHT-920 with the other agonists between these two extremes. Selective inactivation of alpha1-adrenoceptors (achieved by treating yohimbine-protected tissues with phenoxybenzamine) reduced the maximum responses of all agonists, the EC50 values of UK 14304, BHT-920 and noradrenaline and increased the EC50 values of phenylephrine and methoxamine. Prazosin (30 n M ) had no inhibitory effect on responses to low concentrations of BHT-920 and UK 14304 and caused competitive inhibition of responses to phenylephrine and noradrenaline giving pKb values of 8.49 ± 0.18 and 8.23 ± 0.14, respectively. Yohimbine (0.1 μ M ) caused significant competitive inhibition of responses to BHT-920 and noradrenaline with calculated pKb values of 8.43 ± 0.11 for BHT-920 and 7.43 ± 0.31 for noradrenaline and non-competitive inhibition of responses to UK 14304. 2-[2-methoxy-1,4-benzodioxan-2-yl]-2-imidazoline (RX 821002; 10 n M ) caused competitive inhibition of responses to BHT-920 (pKb 9.04 ± 0.27) and dopamine (pKb 8.2 ± 0.2). These data indicate that equine digital veins possess both post-synaptic alpha1 and alpha2-adrenoceptors.  相似文献   

12.
A randomised double-blind clinical trial of 28 horses was undertaken to evaluate the efficacy of isoxsuprine hydrochloride at four different doses:- 0.0 mg/kg bodyweight (bwt) (placebo), 0.6 mg/kg bwt, 1.2 mg/kg bwt and 1.8 mg/kg bwt for treatment of navicular disease. The results showed that horses treated with isoxsuprine hydrochloride (N = 22) responded significantly with respect to clinical assessment score (P less than 0.01) when compared with the control group (N = 6). Furthermore, there were no dose-related differences in the responses of the horses treated with increasing levels of isoxsuprine. No correlation was found between radiological evidence of the extent of navicular disease and severity of lameness or response to treatment.  相似文献   

13.
alpha and beta-adrenergic receptors in detrusor muscle and bladder base of horses were investigated by in vitro responses of smooth muscle strips to exogenous agonist and antagonist drugs. Noradrenaline, isoprenaline and salbutamol induced relaxation of detrusor muscle strips which was significantly inhibited by propranolol and butoxamine suggesting that the response is mediated by beta-2 adrenergic receptors. In the urinary bladder base noradrenaline, phenylephrine and B-HT 920 induced strong contractile effects. These contractile responses were inhibited by the alpha antagonist phenoxybenzamine, the alpha-1 selective antagonist prazosin and the alpha-2 selective antagonist yohimbine. The inhibitory action of prazosin was more potent than that observed with yohimbine suggesting that the response in the bladder base of horses is mediated predominantly by alpha-1 adrenergic receptors, although alpha-2 receptors also participate.  相似文献   

14.
A comparison between the relaxant effects of clenbuterol and theophylline on horse tracheal smooth muscle has been made in vitro. Rat tracheal smooth muscle was also investigated as a reference. The tracheal preparations were initially contracted with carbachol since the smooth muscle did not spontaneously develop tone. The response of the carbachol-contracted preparations to theophylline was the same in the two species. The response to clenbuterol varied. In only five out of eleven horses were the tracheal smooth muscles sensitive to clenbuterol (mean pD2 = 7.92 M). In the remaining six horses the tracheal smooth muscles were insensitive to clenbuterol (mean pD2 = 3.59 M), yet the preparations responded well to theophylline with complete relaxation. All rat tracheal preparations were insensitive to clenbuterol.  相似文献   

15.
This study describes the distribution of vimentin, desmin, smooth muscle actin (SMA) and laminin in the oviduct of the laying domestic fowl. Vimentin immunostaining was localised in the luminal epithelium of the infundibulum, magnum, magnum–isthmus junction and isthmus. The luminal epithelium of the shell gland regions displayed weak vimentin immunostaining. Vimentin immunostaining was demonstrated in the glandular grooves of the tubular infundibular region. In contrast, gland cells in the magnum, isthmus and shell gland regions were vimentin immunonegative. Fibroblasts and vascular endothelial cells in the lamina propria of the oviductal regions studied exhibited vimentin immunostaining. Strong desmin and SMA immunostaining were present in the smooth muscle cells of the tunica muscularis and vascular tunica media. In this study, basement membranes underlying the luminal and glandular epithelia were immunopositive for laminin. In addition, basement membranes associated with smooth muscle cells exhibited laminin immunostaining. The results of the study indicate that the immunolocalisation of desmin, SMA and laminin in the oviduct of the domestic fowl is similar to that in the mammalian uterus. The immunolocalisation of vimentin in the domestic fowl varies depending on the oviductal region.  相似文献   

16.
The contractile activity of the equine large intestine exhibited a biphasic response to feeding: enhancement of migrating complexes passing along the colon and an increase of 50% in cyclic variations in smooth muscle at intervals of 20 min on the left ventral colon for a period of 5 to 7 h postfeeding. The cholinergic agonist, bethanechol (50 micrograms/kg subcutaneously), induced both the migrating complexes and the cyclic variations at intervals of 10-15 min. In contrast, the intra-arterial infusion of PGF2 alpha (3 micrograms/kg/min) increased the contractile activity during infusion, but without inducing distinct patterns of activity. Atropine but not indomethacin or flunixin pre-treatment prevented the effects of postprandial, cholinergic and PGF2 alpha stimulation of colonic motility, suggesting that the gastrocolonic reflex involved mainly cholinergic stimulation of the caecum and replicated colon, including the prostaglandin F2 alpha excitatory effects.  相似文献   

17.
In this study, beta-adrenoceptors of intact equine lymphocytes were identified and subclassified by (-)-[125I]-iodocyanopindolol (ICYP) binding. ICYP binding to intact equine lymphocytes was rapid, saturable (maximal number of binding sites 320 +/- 20 ICYP binding sites/cell, n = 12) and of high affinity (KD value for ICYP 14.4 +/- 1.7 pmol/l, n = 12). Binding was stereospecific as shown by the 10 times greater potency of (-)-propranolol to inhibit binding than its (+)-isomer. Beta-adrenoceptor agonists inhibited ICYP binding with an order of potency: (-)-isoprenaline >(-)-adrenaline >(-)-noradrenaline; the same order of potency was obtained for agonist-induced stimulation of lymphocyte cyclic AMP content. The selective beta2-adrenoceptor antagonist ICI 118,551 was about 1000 times more potent in inhibiting ICYP binding than was the beta1-selective adrenoceptor antagonist CGP 20712A. It is, therefore, concluded that in intact equine lymphocytes, ICYP labels a class of functional beta-adrenoceptors that belong predominantly (>90%) to the beta2-adrenoceptor subtype; a small (<10%) beta1-adrenoceptor component, however, cannot be ruled out completely. ICYP binding to equine lymphocytes might be a suitable model to study function and regulation of the beta-adrenoceptor system in the horse in vivo. The aim of this study was to characterise the beta-adrenoreceptor subtypes present on equine lymphocytes.  相似文献   

18.
A study was undertaken to determine the presence and distribution of alpha- and beta-adrenoceptors in the sheep bladder body and base. In the bladder body, noradrenaline and isoproterenol induced relaxation which was significantly inhibited by propranolol, pafenolol and butoxamine. In the presence of propranolol (10(-5) M), noradrenaline induced a small contraction, as well as phenylephrine, but B-HT 920 failed to cause any effect on the bladder body. In the bladder base, noradrenaline caused a contraction that was significantly inhibited by prazosin but not by yohimbine. Phenylephrine also induced a contractile response in this structure which was inhibited by prazosin. Isoproterenol caused a relaxation that was significantly inhibited by propranolol and pafenolol but not by butoxamine. Relaxation was mediated by both beta 1 and beta 2-adrenoceptors in the detrusor muscle and by beta 1-adrenoceptors in the bladder base. Alpha 1-adrenoceptors contributed to maintain the detrusor tone and contract the bladder base.  相似文献   

19.
Despite ingenious concepts, there are no unequivocal clues as to what, when, and how some undefined biochemical factor(s) or constituent(s) that localizes in the arterial wall can precipitate a thromboatheromatous lesion or arterial disease. The present study focused on the extraction, partial purification, and characterization of a collagen-active platelet stimulator from the aortas of aged burros. The aggregator moiety in the aorta extracts invariably had a higher affinity for platelets in citrated platelet-rich plasma of human beings than for platelets of homologous burros. The platelet-aggregating factor(s) in the aorta extract was retained by incubation with alpha-chymotrypsin. Platelet-aggregating activity was rapidldy abolished after incubation with collagenase, as determined by plateletaggregometry tests. Evidence based on light microscope and polysaccharide histochemical reactions indicates a probability that the intracellular amorphous matrix (PAS-positive) and filamentous components (PTAH-positive) expelled from smooth muscle cells disrupted during homogenization of the aorta may be a principle source of a precursor collagen species which is a potent inducer of platelet aggregation.  相似文献   

20.
The plasma concentration of prolactin in immature cockerels was increased between 10 and 40 min after the intravenous administration of prostaglandin (PG) F2 alpha (200 micrograms/kg body weight). Lower doses had no effect on plasma prolactin concentration. The addition of PGF2 alpha (10(-9) to 10(-6) M) to incubation media had no effect on the basal release of pituitary prolactin but reduced the release of prolactin from pituitary-hypothalamus co-incubations. The addition of noradrenaline (10(-7) M), serotonin (10(-7) M), acetylcholine (10(-6) M) or histamine (10(-6) M) to the co-incubation increased the hypothalamus-induced prolactin release, although these effects were not observed in the presence of 10(-7) M PGF2 alpha. The in vitro release of pituitary prolactin was increased by adding chicken hypothalamic extract in the presence or absence of PGF2 alpha. These results suggest a dual effect on PGF2 alpha of prolactin secretion in the fowl; its stimulation in vivo may result from a peripheral action.  相似文献   

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