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P. Pakarinen and I. Huhtaniemi


The responses of gonadotrophin gene expression, pituitary content and serum levels to castration alone and castration plus testosterone replacement (silicone elastomer implants) were compared in male rats at 10, 30, 60 and 90 days of age. Sham-operated animals served as controls. In addition, 30-day-old castrated rats were treated with dihydrotestosterone (DHT) and diethylstilboestrol (DES). When killed 7 days after castration, the increases in serum LH (six- to eightfold; P < 0·01) and FSH (two- to fourfold; P < 0·01) were similar at all ages studied. Likewise, testosterone reversed the effects of castration in a largely similar fashion at all ages. In contrast, great age-related differences were observed in the responses of gonadotrophin subunit mRNAs to the treatments. Castration increased the common α subunit mRNA two- to fourfold on days 10 and 30 (P < 0·01), sixfold on day 60 (P < 0·01), but not at all on day 90. Testosterone reversed the increases at all ages, but the levels were below those of controls only at 90 days (P < 0·01). The highest increases (sixfold; P < 0·01) of LH-β mRNA were seen on days 10 and 60, the others being two- to threefold higher (P < 0·05–0·01). Testosterone reversed this effect at 60 days and suppressed LH-β mRNA to below the control levels at other ages (P < 0·01). Castration had no effect on FSH-β subunit mRNA at 30 and 90 days but a four-to fivefold increase was seen on days 10 and 60 (P < 0·01). Testosterone suppressed these mRNAs at all ages, and they decreased to below the levels in controls at 30 and 60 days. Testosterone, DHT and DES had, at 30 days, practically the same effects on the LH parameters, whereas DHT was clearly less effective than testosterone and DES in suppressing those of FSH. In conclusion, although there was, in general, good agreement between gonadotrophin mRNA and serum levels in response to castration and testosterone replacement, there were specific ages when the post-castration increases in FSH and/or LH occurred with no detectable change in the respective mRNA levels. These findings indicate that altered transcription (or mRNA stability) is not solely responsible for the responses of the gonadotrophins to altered gonadal feedback, but that changes in translation efficiency and/or serum gonadotrophin stability are involved at specific ages of development.

Journal of Endocrinology (1992) 135, 507–515

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BP Setchell, P Pakarinen, and I Huhtaniemi

The purpose of this study was to assess the concentrations of LH that Leydig cells are exposed to upon in vivo stimulation of steroidogenesis. The concentrations of LH were measured in rats in testicular interstitial extracellular fluid, seminiferous tubular fluid and blood plasma from testicular veins from one testis before and from the other testis of the same rats after an intravenous injection of gonadotrophin-releasing hormone (GnRH) or saline, and compared with the concentrations in blood plasma from a peripheral vein. The concentrations of LH in interstitial fluid surrounding the Leydig cells before the injections were about 10% of the levels in blood plasma, and showed no significant rise at 15 min and a much smaller rise at later times in rats injected with GnRH than those seen in blood plasma from either of the two sources, which were similar. The concentrations of LH in tubular fluid were even lower and showed no change after GnRH. Testosterone concentrations in testicular cells, interstitial fluid and testicular venous blood plasma were significantly increased by 15 min after GnRH, when compared with saline-injected controls, with no change in the levels in tubular fluid. The rise in testosterone concentrations in testicular venous plasma after GnRH was smaller than those in the cells and interstitial fluid. In conclusion, the concentrations of LH reaching the testicular interstitial fluid were only about one-tenth of that measured in the circulation, presumably because the endothelial cells restrict access of the hormone to the interstitial fluid. This indicated that either the Leydig cells are extremely sensitive to LH stimulation or that testicular endothelial cells modulate the action of LH on the Leydig cells.