Fecal adrenal hormone patterns during ovulatory and non-ovulatory reproductive cycles in female veiled chameleons (Chamaeleo calyptratus)

Abstract

The relationship between the reproductive (hypothalamic-pituitary-gonadal; HPG) and adrenal (hypothalamicpituitary-
adrenal; HPA) hormone axes is complex and can vary depending on the species and environmental
factors affecting an individual. In an effort to understand this relationship in female veiled chameleons (Chamaeleo
calyptratus), the patterns of fecal metabolites of corticosterone (C), estradiol (E), testosterone (T), and
progesterone (P) were analyzed by enzyme immunoassay (EIA) during ovulatory (OC; eggs laid) and nonovulatory cycles (NOC; no eggs laid). Glucocorticoid (GC) metabolites in the fecal extracts were characterized by HPLC and corticosterone EIA performance was assessed by parallelism, accuracy and precision tests. The results indicated that the assay chosen reliably measured the hormone metabolites present in the fecal extracts. Regular, cyclical hormone metabolite patterns consisting of an E peak followed by peaks of T, P and C in close succession were observed during both ovulatory and non-ovulatory cycles; relative levels of P and C, however, were higher during ovulatory cycles. Corticosterone metabolite levels, in particular, increased throughout vitellogenesis and peaked in late vitellogenesis (in non-ovulatory cycles) or around the time of ovulation, and remained elevated throughout the gravid period, falling just prior to oviposition. The results provide evidence of variation in glucocorticoid production throughout different stages of the reproductive cycle, including a role in the ovulatory process; the physiology, however, remains unclear.