I P Callard

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Adequate evidence exists to suggest the importance of temporal changes in steroid hormone ratios in the normal reproductive/vitellogenin cycle in oviparous and viviparous elasmobranchs and reptiles. In oviparous species, where the cycle is relatively short, secretion of gonadal hormones is synchronous; thus inhibitory actions of progesterone (P) on hepatic(More)
In non-mammals, estrogen-induced yolk precursors produced by the adult female liver are the main nutritional source for development. Evidence exists that progesterone exerts counter-regulatory effects on estrogen-induced vitellogenesis, and we have used the turtle model (Chrysemys picta) to study changes in hepatic progesterone receptor during the(More)
Anterior pituitary glands from ovulating Japanese quail (Coturnix coturnix) were used to investigate variation in sensitivity to chicken luteinizing hormone-releasing hormone (cLHRH I; Gln8-LHRH). Grouping the pituitaries by ovulatory stage provided preliminary evidence of changes in sensitivity to LHRH during the ovulatory cycle. Pituitaries taken from(More)
Significant changes in % free serum E2, T and P were observed during the annual cycle of the turtle. In contrast no significant changes in SHBG affinity constants (2.29-4.48 x 10(8) M-7) were found and binding capacity for estradiol 17B was between 3.47 and 3.96 x 10(-7) M except in preovulatory animals (2.00 +/- 0.25).
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