Assessment of Urinary Sex Steroids and Oviposition in Response to Intranasal Administration of GnRHa in Fowler's Toads (Anaxyrus fowleri)

MSU Affiliation

College of Agriculture and Life Sciences; Department of Biochemistry, Nutrition and Health Promotion; College of Forest Resources; Department of Wildlife, Fisheries and Aquaculture

Creation Date

2026-07-30

Abstract

Non-invasive methods for hormone administration are increasingly used in amphibian captive breeding, yet the steroidogenic responses to these treatments remain poorly characterized. Understanding hormone-induced steroid production is crucial for optimizing the timing of ovulation, oviposition, and fertilization to improve reproductive success in conservation programs. This study evaluated whether intranasal administration of a gonadotropin-releasing hormone analog (GnRHa) induces ovulation and oviposition in female Fowler's toads (Anaxyrus fowleri) and characterized associated changes in urinary sex steroids. Ten females with follicular development Grades 2–3, observed via ultrasonography, received a resolving dose of 0.4 μg/g GnRHa intranasally, following a prior placebo (30 μl PBS) trial in which each animal served as its own control. Urine was collected at 12 time points over 96 h in both PBS and GnRHa trials, and urinary testosterone and estrone metabolites were quantified by enzyme immunoassay and normalized to creatinine. Follicular development was monitored daily by ultrasonography, and ovulation was assessed visually. Intranasal GnRHa did not induce oviposition in any female, and most individuals showed no change in follicular grade; three females exhibited reduced ultrasound grades at 48–72 h, suggesting limited follicular progression. Nonetheless, GnRHa treatment produced measurable elevations and temporal shifts in urinary testosterone and estrone compared to PBS controls, indicating activation of the hypothalamic–pituitary–gonadal axis, despite the absence of egg laying. These results demonstrate that intranasal GnRHa at 0.4 μg/g is insufficient to trigger oviposition in A. fowleri, but urinary sex steroid monitoring provides a sensitive, non-invasive tool for assessing endocrine responses and refining assisted reproductive protocols for Bufonid species in managed care.

Publication Date

6-17-2026

Publication Title

Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology

Publisher

Elsevier

Rights

© 2026 The Author(s)

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Digital Object Identifier (DOI)

https://doi.org/10.1016/j.cbpa.2026.112034