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  • Title: Changes in plasma steroid levels after single administration of hCG or LHRH agonist analogue in dog and rat.
    Author: Tremblay Y, Belanger A.
    Journal: J Steroid Biochem; 1985 Mar; 22(3):315-20. PubMed ID: 2581068.
    Abstract:
    The present study was designed to investigate the effect of acute administration of gonadotropin on testicular steroid secretion in dog and rat. Animals received a subcutaneous injection of 25 IU/kg of hCG or 1.5 microgram/kg of [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide (LHRH-A). Testosterone is the predominant steroid measured, in dog plasma, under basal conditions. After LHRH-A injection, testosterone levels are not significantly changed while dehydroepiandrosterone and androst-5-ene-3 beta,17 beta-diol (delta 5-steroids) levels are stimulated by almost 20-fold (P less than 0.01). When dogs were injected with hCG, we also observed a marked stimulation of dehydroepiandrosterone levels (20-fold; P less than 0.01) accompanied by a small increase of plasma testosterone concentration (2-fold, P less than 0.01). In rats injected with either hCG or the LHRH analogue, an increment of plasma testosterone (7-fold, P less than 0.01) is detected in the first hour while plasma dehydroepiandrosterone levels are slightly stimulated. Moreover, in rats injected with hCG, low plasma steroid levels are present between 4-12 h after injection due to testicular desensitization. This marked decrease is then followed by a second peak of steroid secretion 24 h later. Acute testicular steroidogenic responsiveness to hCG on the dog is, however, different: after stimulation, the levels of plasma dehydroepiandrosterone are maintained at a plateau and slowly decline after 24-48 h. Our data indicate that in dogs, stimulation of testicular steroidogenesis leads to an increase of plasma delta 5-steroid levels while the same stimuli cause, in the rat, a stimulation of delta 4-androgen, particularly testosterone.
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