Development of homologous radioimmunoassays for equine growth hormone and equine prolactin and their application to the detection of circulating levels of hormone in horse plasma

Abstract

Summary ― Highly purified and well-characterised preparations of equine prolactin and growth hormone from equine pituitary glands were employed to set up highly sensitive and specific homologous radioimmunoassays (RIA) for the measurement of hormone in horse plasma. The limit of sensitivity of the GH RIA was 1.2 ng/ml with mean intra-and inter-assay coefficients of variation (CV) of 6.6 and 10%, respectively. The sensitivity of the equine prolactin (ePRL) RIA was 0.5 ng/ml with mean intra and inter-assay CV of 9.1 and 15.6%, respectively. Dose-response curves of a crude pituitary gland extract and plasma samples collected from a mare and foal were parallel to the standards and the PRL RIA was clinically validated by administration of thyrotropin-releasing hormone (TRH). Plasma samples taken at 15 min intervals over 24 h from lactating mares gave 24 h mean GH values in the range 5.5 to 7.95 ng/ml. Large intermittent elevations of GH activity were detected. The mean 24 h PRL concentrations were between 3.2-10.4 ng/ml in the lactating animals, with higher concentrations earlier in lactation. Long episodic bursts of PRL were detected.

Prolactin in the Horse: Historical Perspective, Actions and Reactions, and Its Role in Reproduction

“…In contrast to those in the nonpregnant mare, Nett et al [22] reported that prolactin concentrations in mares during gestation were extremely variable with no clear pattern of fluctuation. Similarly, Cahill et al [23] described prolactin concentrations in lactating mares as having long episodic bursts, whereas Worthy et al [20] described them as high and irregular.…”

Hormonal responses to acute exercise, training and overtraining a review with emphasis on the horse

“…As far as we know, no study in horses investigated the relationship between sleep and GH secretion yet. However, several studies describe a greater incidence of GH pulses occurring with the onset of or during the dark period of the day, which might indicate that the majority of GH pulses are formed at night during sleep in horses (20,23). This implies that GH measurements are best obtained at night in order to detect GH pulses.…”

Endocrine Diagnostic Techniques in Equine Reproduction

“…PRL. Several RIA systems have been described for the measurement of equine prolactin (Roser et al 1984, Neuschafer et al 1991, Cahill et al 1994 and recently an enzyme imniuno assay has been adapted for equine samples (Burgmann 1994). Both this heterologous enzyme immuno assay and a homologous I-RIA utilising reagents provided by Dr. AF Parlow, Harbor-UCLA, are used in our laboratory.…”