Foldes A, Maxwell C A, Hinks N T, Hoskinson R M, Scaramuzzi R J
Biochem Pharmacol. 1982 Apr 1;31(7):1369-74. doi: 10.1016/0006-2952(82)90030-2.
As an initial step in investigations of putative differences between central nervous system light-sensitive mechanisms in seasonally shedding and non-shedding breeds of sheep, some beta-adrenoceptor characteristics of Merino sheep pineal glands were determined, using [3H]dihydroalprenolol as the labelled ligand. Overall, a dissociation constant of 17.2 +/- 2.6 nmoles/l and a daytime beta-receptor density of 1.6 +/- 0.3 pmoles/mg were determined at 37 degrees. The binding sites exhibited stereospecificity, saturability and apparent homogeneity. 17 beta-Estradiol and progesterone implants that provided hormone concentrations in the physiological range had no significant effect on pineal beta-receptors in male sheep castrated shortly after birth. Dexamethasone injections, on the other hand, in doses sufficient to loosen the attachment of wool fibres to the skin, resulted in decreased pineal beta-receptor density and increased receptor affinity for dihydroalprenolol. This effect was apparently not mediated by altered plasma catecholamine concentrations, since the glucocorticoid treatment did not affect jugular venous noradrenaline, adrenaline or dopamine levels. The possible involvement of glucocorticoids in the regulation of wool growth could thus have a central neuronal component, medicated via action on pineal beta-adrenoceptors in sheep; however, the existence of the putative gonadal steroid feedback on beta-adrenoceptor-mediated pineal function remains to be demonstrated in this species.
作为研究季节性脱毛和非脱毛品种绵羊中枢神经系统光敏感机制之间假定差异的第一步，使用[³H]二氢阿普洛尔作为标记配体，测定了美利奴绵羊松果体的一些β-肾上腺素能受体特征。总体而言，在37℃下测定的解离常数为17.2±2.6纳摩尔/升，白天β受体密度为1.6±0.3皮摩尔/毫克。结合位点表现出立体特异性、饱和性和明显的同质性。在出生后不久阉割的雄性绵羊中，提供生理范围内激素浓度的17β-雌二醇和孕酮植入物对松果体β受体没有显著影响。另一方面，地塞米松注射剂量足以使羊毛纤维与皮肤的附着松动，导致松果体β受体密度降低，对二氢阿普洛尔的受体亲和力增加。这种作用显然不是由血浆儿茶酚胺浓度改变介导的，因为糖皮质激素治疗不影响颈静脉去甲肾上腺素、肾上腺素或多巴胺水平。因此，糖皮质激素可能参与羊毛生长调节，可能有一个中枢神经元成分，通过对绵羊松果体β-肾上腺素能受体的作用来调节；然而，在这个物种中，假定的性腺类固醇对β-肾上腺素能受体介导的松果体功能的反馈是否存在仍有待证实。
