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Biomedical subjects

R F Seamark

Publications and source records attributed to R F Seamark.

At least 163 records · Page 9Linked to original sources
PubMed1975

Hormone studies on ewes grazing an oestrogenic (Yarloop clover) pasture during the reproductive cycle.

The endocrine function of Merino and Corriedale ewes grazing an oestrogenic (Yarloop clover) pasture has been studied during the oestrous cycle, pregnancy and parturition, and the results compared with those from a study of similar ewes grazing a neighbouring grass pasture. Plasma progesterone, oestrogen and corticoids were measured using competitive protein binding assay procedures. During the oestrous cycle clearly anomalous patterns in hormone content were evident in ewes grazing Yarloop, and this related to their significantly poorer (P less than 0.001) fertility. The first mating, when ewes were 1-1/2 years of age, was particularly affected. Successful conception took place in only 27% of ewes mated on Yarloop, compared with 95% on grass. Evidence of disturbance in the normal patterns of both plasma oestrogen and progesterone was found in infertile ewes, including a shortened period of luteal function. Disturbance of endocrine function caused by Yarloop clover ingestion was also found in pregnant ewes, with the mean plasma progesterone concentrations during the latter half of pregnancy reduced (P less than 0.05) and the plasma oestrogen and corticoid levels tending to be higher in these animals. In detailed hormone studies in the periparturant period, both groups showed a similar fall in plasma progesterone and rise in plasma oestrogen prior to parturition. Where excessive time was taken for parturition (more than 30 min) this was reflected in higher plasma corticoid levels (P less than 0.05) within 8 h of birth.

Adrenal Cortex Hormones↗
PubMed1975

The sheep ovary: regulation of steroidogenic, haemodynamic and structural changes in the largest follicle and adjacent tissue before ovulation.

Important changes occur in the follicle that is destined to ovulate and also in the surrounding ovarian tissue of sheep during the 72 hr preceding ovulation. It is our purpose to describe the morphological and functional changes that take place in large follicles during the preovulatory period and to relate these to the local ovarian environment and general endocrine status prevailing at this time. A consideration of changes in the structure, blood supply and function of the ovaries in vivo, is followed by a discussion of the functional capacity of the individual ovarian components when isolated and studied in vitro. Against this background, the nature and sequence of events that occur in the preovulatory follicle and the mechanisms which regulate them will be discussed.

Adenylyl Cyclases↗