Hormonal Control of Prostatic Thyrotropin-Releasing Hormone (TRH) Testosterone Modulates Prostatic TRH Concentrations

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Abstract
The presence of extremely high concentrations of authentic TRH in the rat prostate lead to investigations of whether prostatic TRH concentrations were under hormonal control. Both the immunoreactive TRH content per prostate and TRH immunoreactivity expressed per 100 mg prostatic protein were lower in animals 2 wk after hypophysectomy than in sham-operated and calorically restricted weight-matched controls. Since many of the prostatic functions are testosterone dependent, the possibility that testosterone modulated prostatic TRH concentrations was assessed. Prostatic TRH concentrations were measured in the following 4 groups of sexually mature male Sprague-Dawley rats: group I, sham operated; group II, castrated; group III, castrated animals with 5-mm Silastic testosterone implants; and group IV, castrated animals with 20-mm testosterone implants. Prostatic TRH concentrations in these 4 groups 2 wk after surgery were 600.5 .+-. 33.3, 65.1 .+-. 22.6, 169.4 .+-. 55.3 and 609.5 .+-. 144.3 (.+-. SE) ng/100 mg protein. There was good linear correlation between prostatic TRH concentrations and serum testosterone concentrations ( r = 0.65; P < 0.01). By subjecting the pooled prostatic extracts from each group to ion exchange chromatography on a SP-Sephadex C-25 column and measuring the proportion of immunoreactivity co-eluting with authentic TRH, the fall in prostatic TRH immunoreactivity after castration and hypophysectomy was indeed due to a loss of authentic TRH. The prostatic TRH concentrations are under hormonal control and appear to be modulated by serum testosterone concentrations. Hormonal regulation of a neuropeptide in a mammalian extrahypothalamic site was demonstrated. A physiological role for this neuropeptide at this site is suggested.

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