Meeting Abstract
Environmental factors and hormones can regulate the development of various physiological systems. Photoperiod, melatonin, and thyroid status are known to affect significantly the reproductive system in seasonal breeders, but effects on the GI tract have not been as well studied. The present studies examined whether constant light (which inhibits melatonin release), oral melatonin administration, and hypothyroidism affect gastrointestinal (GI) development and reproduction in juvenile male rice rats. Rice rats were subjected, in separate experiments, to 14L:10D or constant light (24L:0D) photoperiods, the administration of oral melatonin, or the administration of oral propylthiouracil (PTU; 0.06%) to induce hypothyroidism from 21-56 days of age. The following masses were examined: body, testes, seminal vesicles (SV), Harderian glands (HG), spleen, and wet (W) and dry (D) masses of the stomach (St), small intestine (SI), cecum (Ce), and colon (Co). In addition, small intestine and colon lengths were measured. Constant light significantly reduced only SV and HG masses; there was no effect on any other variable examined. Oral melatonin administration reduced body, testes, SV, HG, WSt, WCo, DCo masses and the SI and Co lengths. Hypothyroidism reduced masses of the body, testes, SV, and HG, while causing decreases in only the WCe and DCe masses. These data show that melatonin most dramatically affects growth, reproduction, and GI development in males, but that constant light and hypothyroidism were without effect on most GI endpoints. It was hypothesized that changes in the GI tract may be a necessary mechanism for coping with likely seasonal changes in metabolic requirements. We are currently examining the effects of daily food restriction on these same variables in males.
