The involvement of calcitonin in the reproductive physiology of the rainbow trout.

Plasma from rainbow trout (Salmo gairdneri) of both sexes was sampled every month throughout an annual reproductive cycle in order to elucidate possible relationships between plasma calcitonin and free and protein-bound calcium and magnesium. This was then studied in greater detail around the time of ovulation in the female fish. The plasma levels of the parameters studied were stable in males during the whole annual cycle and were similar to the levels found in females during at least 6 months of the cycle. Plasma levels of protein-bound calcium and magnesium as well as calcitonin were raised in the females for 6, 4 and 3 months respectively. These increases occurred concomitantly during the months before and after ovulation, but no correlations between the protein-bound ion and calcitonin levels were found during this period. With the exception of a decrease observed in December, the free plasma levels of calcium and magnesium were stable in both males and females throughout the cycle. This decrease was attributed to the high production rate of the yolk-protein precursor vitellogenin, which binds both calcium and magnesium. In the detailed study on the ovulating females, plasma calcitonin levels were high 4 weeks before, and continued to increase until the time of ovulation, when a sharp decrease towards normal was noted. The free plasma calcium and magnesium levels were not affected, while the protein-bound levels of calcium and magnesium were found to decline towards normal for the duration of the experiment, without any obvious correlation with the time of ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)