Graduate Thesis Or Dissertation
 

Reproductive cycle of the male newt Taricha granulosa : exogenous and endogenous regulation of plasma androgens

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  • During a 13-month period starting in October of 1976, adult male rough-skinned newts (Taricha granulosa) were collected periodically to study seasonal changes in reproductive status. Plasma androgen concentration, measured by radioimmunoassay, is elevated during autumn and spring (about 50 ng/ml). Winter and summer levels are considerably lower (less than 10 ng/ml). Seasonal changes in testis composition indicate one annual cycle of evacuation (October- March) and spermatogenetic recrudescence (March-October). Concomitant with decreasing ambient temperature in autumn are the occurrence of second metamorphosis, which includes the assumption of nuptial characteristics such as caudal fins, and the onset of spermiation and sex behaviors. To test the hypothesis that temperature influences plasma androgens through its effects on the pituitary-gonadal axis, newts were maintained at 12° or 18°C for 6 weeks in the laboratory. Androgen levels remained unchanged. Caudal fins regressed in 18°C newts and developed in 12°C newts, suggesting that prolactin, but not luteinizing hormone, was affected by water temperature. To assess the contribution made by the mature testicular zone to plasma androgen levels, newts were subjected to either bilateral total or bilateral hemicastration. Hemicastration involved extirpation of the mature zone from each lobe of each testis. Each testis consists of several lobes; each lobe is comprised of distinct zones of different maturation stages. The mature zone, containing seminiferous lobules that are already evacuated or still contain sperm, was found to produce a significant portion of the plasma androgens.
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