Masters Theses

Date of Award

12-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Comparative and Experimental Medicine

Major Professor

S.M.L. Chamindrani Mendis-Handagama

Committee Members

Jack Oliver, Juergen Schumacher, Jon Wall

Abstract

Leydig cells in the testis are the primary source of androgens in the adult male mammal. Therefore, the process of Leydig cell differentiation during the prepubertal period is essential to establish the Leydig cell population in the adult. Little has been published regarding the factors that regulate the postnatal Leydig cell differentiation in hamsters. However, it has been observed in adult male hamsters that Leydig cells regress under reduced photoperiods, but recrudesce with re-exposure to normal photoperiods. In the present investigation, the effects of light, hypothyroidism, hyperthyroidism, and melatonin treatment on Leydig cell differentiation in the neonatal-prepubertal hamster are investigated. Six treatment groups of male Syrian Golden hamsters were used. Group I male hamsters were raised under regular light conditions (12hr: 12hr Light:Dark) and group II hamsters were raised under reduced light (23hr: 1hr Dark: Light). Hamsters in Groups III received triidothyronine (T3; 50 μg/ kg. bwt); lactating mothers were injected every four days from birth of pups to day 28, and were maintained under regular light conditions. Hamsters in Group IV were maintained under regular light regimes (12hr: 12hr) and were made hypothyroid by adding 0.1% propylthiouracil to drinking water of lactating mothers from birth to day 28. Hamsters in Group V were raised in dark (similar to Group II), but their mothers received T3 injections similar to those in Group III. Lactating mothers in Group VI received melatonin injections (15 milligrams/ kg. bwt) every other afternoon from birth to day 28. Following euthanasia at postnatal day 28, blood was collected from the heart, serum prepared and stored until assay for hormones: thyroxin (T4), and melatonin.

One testis from each hamster in each group was fixed by whole body perfusion, processed and embedded in epon-aradite. Using 1-micron sections that were stained with Methylene Blue-Azure II, Leydig cell numbers per testis in the experimental groups were quantified by the disector method. Leydig cells were identified by their characteristic morphology and their location in the testis interstitium. The ipsilateral testis from each hamster in each group was incubated in media containing luteinizing hormone (100ng/ml) and used to determine testosterone and androstenedione secretory capacity per testis in vitro. There was a reduction in Leydig cell numbers per testis in D28 hamsters (Group II), D28T3 hamsters (Group V), L28PTU hamsters (Group IV), and L28M hamsters (Group VI) when compared to L28 hamsters (Group I) and L28T3 hamsters (Group III). Significantly increased testosterone secretory capacities were found in the hamster groups D28 (Group II) and L28T3 (Group III) when compared to L28 (Group I). There were significantly reduced testosterone secretory capacities in hamsters in L28PTU (Group IV), L28M (Group VI), and D28T3 (GroupV), compared to L28 (Group I).The majority of the groups were not significantly different in androstenedione secretory capacity per testis except there were significantly lower values in L28PTU (Group IV) and D28T3 (GroupV). L28 (Group I) hamsters had significantly higher serum thyroxin levels than hamsters in D28 (Group II), L28PTU (Group IV), L28M (Group VI). Serum melatonin levels were the lowest in L28 (Group I) hamsters and the highest in L28PTU (Group IV) hamsters. These findings demonstrate that increased levels of melatonin and decreased levels of thyroxin negatively regulate and decreased levels of melatonin and increased levels of thyroxin positively regulate Leydig cell differentiation in the prepubertal hamster testis. It is concluded that thyroid pineal interactions are important in regulating the process of postnatal Leydig cell differentiation in the perpubertal hamster testis.

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