A Study of the Effects of Hypothyroidism Induced by Propylthiouracil on Adrenoceptors and Noradrenaline Levels in the Vas Deferens of the Rat

Abstract

1. The anti-thyroid drug, propylthiouracil (0.05% w/v in drinking water) was administered to rats for 3-4 weeks. This treatment decreased the rate at which rats gained body weight but did not affect the weight of the vasa deferentia. Circulating levels of thyroxine and triiodothyronine were markedly decreased.2. The potencies of postjunctional a-adrenoceptor agonists, 1 -noradrenaline and 1-phenylephrine, in eliciting contraction of the epididymal end of the vas deferens were unaffected by propylthiouracil treatment. In contrast, the potency of the 0-adrenoceptor agonist, 1 -isoprenaline, in inhibiting field stimulationinduced twitches of the prostatic end of the vas deferens was decreased in tissues from propylthiouracil-treated rats. Thus hypothyroidism induced by propylthiouracil produced an apparent change in the properties of postjunctional P-adrenoceptors without a concomitant reciprocal change in the properties of postjunctional a-adrenoceptors.3. Treatment of rats with propylthiouracil led to a small increase in the concentration of noradrenaline in the vas deferens, and a concomitant small increase in the rate of accumulation of 3H-noradrenaline in in vitro experiments. Extraneuronal uptake of ' H-isoprenaline was unaffected by propylthiouracil treatment. 4.The potencies of the prejunctional a-adrenoceptor agonists, xylazine and 1 -noradrenalhe, in producing inhibition of twitches evoked by field stimulation of preparations of the prostatic end of the vas deferens, were similar in preparations from propylthiouracil-treated and control rats, although the slope of the log dose-response curve to xylazine was decreased in the former group. Thus unequivocal changes in the properties of prejunctional a-adrenoceptors did not accompany the other prejunctional effects of propylthiouracil upon endogenous noradrenaline levels and neuronal uptake of H-noradrenaline in this organ.

Adrenoreceptor‐mediated Responses in the Isolated Portal Vein of the Hypothyroid Rat

“…Rats from control and hypothyroid groups were killed by a blow on the head and the portal vein dissected free from peritoneum and fat. A section approximately 5 mm in length was removed, slit open and set up in a 30 ml organ bath containing a modified Kreb's solution of the following composition (mmol I-'): NaC1, 118.05; KCl, 4.69; MgS04, 0.45; KH2P04, 1.18; NaHC03, 25.00; glucose, 11.66; CaC12, 2.52; disodium edetate, 0.03; sodium ascorbate, 0.09 (Leedham, Handberg, Ishac & Pennefather, 1981). The use of anti-oxidants avoids t h e possibility that differences in the tissue levels of thyroid hormone from the two experimental groups may directly influence estimates of the potency of catecholamines by their chelation of copper ions (Shida, Meyers & Barker, 1963).…”

Effect of Induced Thyroid Dysfunction upon Uterine Responsiveness in Strips from Pregnant and Nonpregnant Rats

“…It has been proposed that triiodo thyronine (T3) could directly act on the uterus since in hypophysectomized animals T3 administration was effective in restoring uterine responsiveness to estrogen [2], In ad dition. binding studies carried out on rat uterine tissue homogenate support the hy pothesis that this organ is directly regulated by thyroid hormone levels [3,4] in a similar way to that observed in other target tissues [5,6], Furthermore, it is well known that thy roid hormones influence agonist-mediated responses in several tissues, including the heart [7,8], vas deferens [9] and liver [10]. It is suggested that thyroid hormone-depen dent changes in tissue responses to agonists could result from changes at the receptor level and/or potentiation of intracellular events distal to receptor activation [11,12].…”