The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

Heady Tales of Ewe (#112)

Iain Clarke 1
  1. Neuroscience Program, Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Melbourne, VIC, Australia

In 1969, James R Goding et al published a paper describing what was arguably the first radio-immunoassay for luteinising hormone (LH) – a considerable advance on the ovarian ascorbic acid depletion test! This paper also reported that a single injection of estradiol caused a surge in LH secretion, synonymous with the preovulatory surge. This and other papers heralded a new era in reproductive biology, enabling easy measurement of hormones. Following shortly afterwards (in 1971), the structure of gonadotropin releasing hormone (GnRH) was published simultaneously by Guilleman and Schally. It was hypothesised that brain secretion of GnRH into the hypophysial portal blood system was responsible for the synthesis of the gonadotropins and secretion of the same, but it was some years before this was conclusively demonstrated. George Fink and colleagues were the first to measure GnRH surges in anesthetised rats, in 1977. As a young hopeful Australian Wool Corporation Fellow, I was fortunate to make the acquaintance of James T Cummins, a neurosurgeon. Jim and I devised a means of surgically accessing the portal blood system in the sheep and we were able to collect blood flowing out of the median eminence from sentient animals in real time. To our great satisfaction, we were able to measure GnRH in this portal blood and we then proceeded to describe the pattern of pulsatile GnRH secretion in conscious animals, including the estrogen-induced surge. The ensuing years allowed me to capitalise on this and other surgical procedures, to detail steroid feedback effects and the influence of season, stress and metabolic state on the secretion of GnRH and the gonadotropins. This paper will review highlights and landmarks of 40 years research on reproductive neuroendocrinology in the ewe.