Effects of clonidine in the isolated rat testicular capsule

Abstract

The testicular capsule contracts in response to noradrenaline and adrenaline, but the effects of adrenoceptor agonists, as for instance clonidine, had not yet been thoroughly evaluated. The testicular capsule from adult male Wistar rats was isolated and mounted in organ bath and cumulative concentration curves were performed for clonidine and other adrenergic agonists in the absence or presence of α-adrenoceptors antagonists. The order of potency for agonists (pD2) was clonidine=adrenaline>UK 14,304>noradrenaline>phenylephrine>methoxamine. The consecutive curves for clonidine showed desensitization with 3-fold rightward shift and Emax reduction of 40%. The noradrenaline curves were 4.5, 19 and 190-fold less potent after clonidine pretreatment at 10−5, 10−4 or 10−3 M for 10 min, respectively, added to Emax decrease by about 20%. Clonidine (10−5 M for 10 min) was unable to alter the noradrenaline curves if the treatment was made in the presence of idazoxan (α2-adrenoceptor antagonist) whereas prazosin (α1-adrenoceptor antagonist) was ineffective. The effect of idazoxan 3×10−7 M on noradrenaline curves was decreased by 50% after clonidine pretreatment, as reflected by the concentration ratio of 5.2±1.2 (treated tissue) and 10.1±1.0 (untreated tissue). However, the concentration ratio for prazosin 3×10−8 M was unchanged. After phenoxybenzamine (irreversible antagonist of α1-adrenoceptor) pretreatment, the residual noradrenaline contraction was antagonized by idazoxan or prazosin with pKB values of 7.8 and 5.1, respectively. The results indicate the presence of α2-adrenoceptors in testicular capsule. Furthermore, these receptors may be desensitized by clonidine, causing a decreased potency of noradrenaline.

Effect of Venlafaxine, Pramipexole, and Valsartan on Spermatogenesis in Male Rats

“…More specifically, the use of medication for a longer time period brutally affects the male fertility, while the short courses of medication caused temporary infertility. 5 …”

“…More specifically, the use of medication for a longer time period brutally affects the male fertility, while the short courses of medication caused temporary infertility. 5 The spermatogenesis is the process of development of spermatozoa through a series of multiple events. In testes, the process of spermatogenesis takes place in the lumen of seminiferous tubules, and almost 90% of testes consist of seminiferous tubules.…”

Effects of dipyrone and acetylsalicylic acid on contractions of distal cauda epididymis duct, serum testosterone and sperm count in rats

“…Additionally, pharmacological parameters E max (maximal contraction) 35,40 and pEC 50 (agonist potency ‐ the negative log of EC 50 ) 41 were graphically determined from concentration response curves in order to allow comparisons between agonist curves in the absence or presence of dipyrone or ASA.…”

Validation of canine uterine and testicular arteries for the functional characterisation of receptor-mediated contraction as a replacement for laboratory animal tissues in teaching

“…There are limited studies evaluating receptor classification in testicular arteries, particularly in the canine model. However, one study indicated that α 2 -adrenoceptors likely contribute to smooth muscle contraction in the rat testicular capsule [23]. As it has been shown that canine vessels in different body regions have varied α-adrenoceptor subtypes [24], it is likely that α 2adrenoceptors may be more prominent in canine testicular arteries.…”