scholarly journals Mediation of contraction in rat cauda epididymidis by alpha-adrenoceptors

Reproduction ◽  
2002 ◽  
pp. 887-892 ◽  
Author(s):  
G Chaturapanich ◽  
S Maythaarttaphong ◽  
V Verawatnapakul ◽  
C Pholpramool
Keyword(s):  
Pressure Transducer ◽  
Systemic Effects ◽  
Alpha Adrenoceptors ◽  
Alpha Adrenoceptor ◽  
Adrenoceptor Antagonist ◽  
Alpha Adrenoceptor Agonists ◽  
Adrenoceptor Agonists ◽  
Cauda Epididymidis ◽  
Spontaneous Contractions

Subtypes of alpha-adrenoceptors responsible for contractions of the rat cauda epididymidis were studied in vivo by micropuncture using a servo-nulling pressure transducer system. Administration of both non-selective and selective alpha-adrenoceptor agonists in doses of 1-40 microg noradrenaline kg(-1) body weight (BW), 1-100 microg clonidine kg(-1) BW, or 100-800 mg methoxamine kg(-1) BW enhanced contractions of the proximal cauda epididymidis in a dose-response manner. The potency of the agonists were noradrenaline > or = clonidine>methoxamine. Pre-treatments with selective alpha(1)-adrenoceptor antagonist (prazosin) and alpha(2)-adrenoceptor antagonist (yohimbine) at the doses of 400 and 800 microg kg(-1) BW, respectively, had very little effect on spontaneous contractions, but effectively blocked the responses to the maximal doses of methoxamine and clonidine. The responses could not be explained by the systemic effects of agonists and antagonists. The results suggest that contraction of the proximal cauda epididymidis of rats is mediated by both alpha(1)- and alpha(2)-adrenoceptors. The latter appears to be more abundant.

Evidence for existence of postjunctional alpha 1- and alpha 2-adrenoceptors in cat pulmonary vascular bed

1985 ◽  
Vol 249 (4) ◽  
pp. H891-H898
Author(s):  
A. L. Hyman ◽  
P. J. Kadowitz
Keyword(s):  
Adrenergic Nerve ◽  
Alpha Adrenoceptor ◽  
Adrenoceptor Antagonist ◽  
Vascular Bed ◽  
Alpha Adrenoceptor Agonists ◽  
Adrenoceptor Blocker ◽  
Adrenoceptor Agonists ◽  
Uk 14,304 ◽  
6 Hydroxydopamine ◽  
Pulmonary Vascular Bed

The subtypes of postjunctional alpha-adrenoceptors in the feline pulmonary vascular bed were studied using selective alpha-adrenoceptor agonists and antagonists. Under conditions of controlled pulmonary blood flow and constant left atrial pressure, intralobar injections of the alpha 1-adrenoceptor agonists, phenylephrine and methoxamine, and the alpha 2-adrenoceptor agonists, UK 14,304 and BHT 933, increased lobar arterial pressure in a dose-related manner. Prazosin, an alpha 1-adrenoceptor antagonist, reduced responses to phenylephrine and methoxamine to a greater extent than responses to UK 14,304 and BHT 933. Yohimbine, an alpha 2-adrenoceptor blocker, decreased responses to UK 14,304 and BHT 933 without altering responses to phenylephrine or methoxamine. The same pattern of blockade was observed in animals pretreated with 6-hydroxydopamine, an agent that destroys the integrity of adrenergic nerve terminals. However, in propranolol-treated animals, prazosin antagonized responses to phenylephrine and methoxamine without altering responses to UK 14,304 or BHT 933, and the selectivity of the blocking effects of yohimbine were preserved. Responses to intralobar injections of norepinephrine were markedly decreased by prazosin, whereas yohimbine had only a small effect. These data suggest the presence of both postjunctional alpha 1- and alpha 2-adrenoceptors mediating vasoconstriction in the pulmonary vascular bed. These results also indicate that the vasoconstrictor responses to injected norepinephrine in the cat pulmonary vascular bed are due mainly to activation of alpha 1-adrenoceptors.

Effects of α-adrenoceptor agonists and antagonists on thyroid hormone secretion

1985 ◽  
Vol 108 (2) ◽  
pp. 184-191 ◽  
Author(s):  
Bo Ahrén
Keyword(s):  
Thyroid Hormone ◽  
Dose Level ◽  
Hormone Secretion ◽  
High Dose ◽  
Inhibitory Effects ◽  
High Dose Level ◽  
Adrenoceptor Antagonist ◽  
Adrenoceptor Agonist ◽  
Adrenoceptor Agonists

Abstract. The effects of various α-adrenoceptor agonists and antagonists on blood radioiodine levels were studied in mice pre-treated with 125I and thyroxine. The non-selective α-adrenoceptor agonist noradrenaline and the selective α1-adrenoceptor agonist phenylephrine both enhanced blood radioiodine levels. Noradrenaline was more potent than phenylephrine. Contrary, the selective α2-adrenoceptor agonist clonidine depressed basal levels of blood radioiodine. The non-selective α-adrenoceptor antagonist phentolamine and the selective α1-adrenoceptor antagonist prazosin both inhibited the noradrenaline-induced elevation of radioiodine levels, whereas the α2-adrenoceptor antagonist yohimbine had no such effect, except at a high dose level. All three α-adrenoceptor agonists, noradrenaline, phenylephrine and clonidine, inhibited the radioiodine response to TSH. In addition, TSH-induced increase in radioiodine levels was inhibited by prazosin, whereas yohimbine had no effect. Phentolamine inhibited the radioiodine response to TSH when given 2 h prior to TSH, whereas when given 15 min prior to TSH the response to TSH was potentiated by Phentolamine. It is concluded, that under in vivo conditions in the mouse, α1-adrenoceptor activation stimulates basal thyroid hormone secretion and inhibits TSH-induced thyroid hormone secretion. Further, α2-adrenoceptor activation inhibits basal thyroid hormone secretion. In addition, TSH-induced thyroid hormone secretion is inhibited by α1-adrenoceptor antagonism. Thus, α-adrenoceptors induce both stimulatory and inhibitory effects of thyroid function.

scholarly journals Pathogenesis of Arterial Lesions Induced by Dopaminergic Compounds in the Rat

1989 ◽  
Vol 17 (1_part_2) ◽  
pp. 203-213 ◽  
Author(s):  
William D. Kerns ◽  
Emanuel Arena ◽  
Richard A. Macia ◽  
Peter J. Bugelski ◽  
William D. Matthews ◽  
...  
Keyword(s):  
Arterial Injury ◽  
Mesenteric Arteries ◽  
Receptor Subtypes ◽  
Alpha Adrenoceptors ◽  
Beta Adrenoceptor ◽  
Alpha Adrenoceptor ◽  
Alpha Adrenoceptor Agonists ◽  
Arterial Lesions ◽  
Vascular Beds ◽  
Renal Vascular

Fenoldopam mesylate (FM), a selective post-junctional dopaminergic (DA1) vasodilator, causes lesions of large caliber splanchnic arteries (100–800 μm) in the rat characterized by necrosis of medial smooth muscle cells and hemorrhage. FM does not induce lesions in other vascular beds of the rat, or in dogs or monkeys. Dopamine, like FM, causes hemorrhagic lesions of large caliber splanchnic arteries in the rat, as well as fibrinoid necrosis of small caliber arteries (<100 μm) of the splanchnic, cerebral, coronary and renal vascular beds. Dopamine is an alpha- and beta-adrenoceptor and a dopaminergic receptor agonist. Because these arterial lesions are thought to result from the pharmacologic activity of these 2 compounds, we sought to ascertain the presence of DA1 receptors in mesenteric arteries of the rat and to determine the role of these or other vascular receptor subtypes in lesion induction. We also studied the process of repair after arterial injury caused by FM or dopamine. The presence of DA1 receptors was confirmed in isolated perfused mesenteric arteries by standard pharmacologic techniques; stimulation by FM resulted in vasodilation which was inhibited by the DA1 receptor antagonist SK&F 83566-C. Likewise, SK&F 83566-C prevented the induction of hemorrhagic lesions of large caliber arteries in rats upon infusion of FM or dopamine. In rats co-exposed to the alpha-adrenoreceptor antagonist phenoxybenzamine (PBZ) and either FM or dopamine, the incidence and severity of hemorrhagic lesions of large caliber arteries were increased, but PBZ prevented the formation of dopamine-induced fibrinoid lesions in arteries of small caliber. Rats exposed concurrently to dopamine, phenoxybenzamine, and SK&F 83566-C were free of all arterial lesions. Thus, the induction of splanchnic arterial lesions in the rat by dopamine and FM is caused by stimulation of, and interaction between, alpha-adrenoceptors and dopaminergic DA1 receptors. Fibrinoid lesions of small arteries (alpha-adrenoceptor-mediated) were repaired, as observed morphologically by 14 d after exposure to dopamine. Hemorrhagic lesions of large caliber arteries (DA1 receptor-mediated) had undergone significant repair by 28 d after exposure to FM but these arteries possessed a thicker media surrounded by adventitial fibrosis. Thus, morphologically distinct receptor-mediated splanchnic arterial lesions induced by dopaminergic and alpha-adrenoceptor agonists follow a markedly different course of repair. Arterial lesions induced by FM or dopamine by activation of post-junctional dopaminergic DA1 receptors may represent a model of polyarteritis nodosa.

Quantitative relationships between .alpha.-adrenergic activity and binding affinity of .alpha.-adrenoceptor agonists and antagonists

1984 ◽  
Vol 27 (4) ◽  
pp. 495-503 ◽  
Author(s):  
Pieter B. M. W. M. Timmermans ◽  
Adriaan De Jonge ◽  
Martin J. M. C. Thoolen ◽  
Bob Wilffert ◽  
Harry Batink ◽  
...  
Keyword(s):  
Binding Affinity ◽  
Alpha Adrenoceptor ◽  
Alpha Adrenoceptor Agonists ◽  
Adrenergic Activity ◽  
Adrenoceptor Agonists

Coronary vasoconstriction mediated by alpha 1- and alpha 2-adrenoceptors in conscious dogs

1987 ◽  
Vol 253 (2) ◽  
pp. H388-H393 ◽  
Author(s):  
O. L. Woodman ◽  
S. F. Vatner
Keyword(s):  
Conscious Dogs ◽  
Similar Degree ◽  
Coronary Resistance ◽  
Coronary Vasoconstriction ◽  
Beta Adrenoceptor ◽  
Alpha Adrenoceptor ◽  
Alpha Adrenoceptor Agonists ◽  
Vasoconstrictor Response ◽  
Adrenoceptor Agonist ◽  
Adrenoceptor Agonists

Coronary vasoconstriction was examined in response to the selective stimulation of alpha 1- and alpha 2-adrenoceptors in chronically instrumented conscious dogs. Norepinephrine (NE, 0.05 and 0.1 micrograms X kg-1 X min-1), a mixed alpha 1- to alpha 2-adrenoceptor agonist, phenylephrine (PE, 0.5 and 1.0 micrograms X kg-1 X min-1), a preferential alpha 1-adrenoceptor agonist, and B-HT 920 (1.0 micrograms X kg-1 X min-1), a preferential alpha 2-adrenoceptor agonist, were infused intravenously after ganglionic (hexamethonium, 30 mg/kg iv), beta-adrenoceptor (propranolol, 1.0 mg/kg iv), and muscarinic receptor (atropine methylbromide, 0.1 mg/kg iv) antagonism. Equipressor doses of the alpha-adrenoceptor agonists caused similar increases in calculated late diastolic coronary resistance (NE, 0.57 +/- 0.10 mmHg X ml-1 X min; PE, 0.61 +/- 0.13 mmHg X ml-1 X min; B-HT 920, 0.64 +/- 0.09 mmHg X ml-1 X min). Mechanically increasing aortic root pressure to levels similar to those observed in response to alpha-adrenoceptor stimulation did not increase coronary resistance. Preferential antagonism of alpha 1-adrenoceptors with prazosin (1 mg/kg iv) abolished the vasoconstrictor response to PE but had a lesser effect on the response to B-HT 920. Antagonism of alpha 2-adrenoceptors with rauwolscine (alpha-yohimbine, 0.1 mg/kg iv) abolished the vasoconstrictor response to B-HT 920 but had a lesser effect on the response to PE. The response to NE was reduced to a similar degree by either alpha 1- or alpha 2-adrenoceptor antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

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