Date of Award:

5-1-1983

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

LeGrande C. Ellis

Committee

LeGrande C. Ellis

Committee

Warren C. Foote

Committee

Raymond Sanders

Committee

Donald Sisson

Abstract

The purpose of this study was to determine seasonal patterns of five hormones in male mink of three different color phases during a year-long observation period. Four statistically significant pulses of cortisol were observed on November 4, February 3, April 28 and June 9. These adrenocorticoid peaks of activity corresponded with similar peaks of plasma ACTH. Concomitant with the fall and spring pelage changes (moults), α-MSH secretion was high from September through November and from May through June, but was reduced during the winter months except for a small secondary rise in January and February. Cortisol, ACTH and α-MSH levels correlated very strongly with the autumnal and spring moults. Pastel mink had lower α-MSH levels than did opal or dark mink. Plasma ß-endorphin and ß-lipotropin levels were inversely related to each other. ß-endorphin was high in the fall and spring while ß-lipotropin was low during the corresponding period, but high in the winter months. These results indicated that there was differential processing of ß-lipotropin into ß-endorphin in the body. α-MSH and ß-endorphin levels were low prior to and during the breeding season. Parallel secretion of ACTH and ß-endorphin was observed with seasonal differences. Moribund dark mink kits were found to have high body levels of ß-endorphin and high head levels of ß-lipotropin suggestive of a genetic mechanism for increased ß-lipotropin secretion and a its conversion to ß-endorphin in the body. The cause of the death of the mink kits was believed to be due to increased ß-endorphin and ACTH secretion that brought about a concomitant depletion of energy stores with hypothermia, dehydration and loss of appetite. N-acetyltransferase (NAT) activity and serum melatonin demonstrated a diurnal rhythm with NAT activity and serum melatonin levels being higher during the hours of darkness and lowest during the day. Hypothalamic MAO was highest at 11:00am and 8:00pm. These results were consistant with the previous findings that the furring and reproductive cycles are regulated by photoperiod. Shifting of melatonin peaks due to natural changes in daylength was postulated as being the Zietsgeber for entraining the biological clocks for pelage and reproductive changes.

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