Micro-Determination of Corticosteroids in Ovine Peripheral Plasma: Effects of Venipuncture, Corticotrophin, Insulin and Glucose

This paper describes experiments with sheep, in which changes in plasma cortisol, after imposition of various stressor agents, were compared to the changes following administration of synthetic ACTH. The influence of stress associated with shearing, yarding, oestrogen administration (30 Jlg oestradiol benzoate, i.v.), feeding and fasting on the plasma concentration of cortisol was monitored in four mature Merino ewes. They were placed in the experimental environment for 21 days before monitoring began. The ewes were treated in pairs, each pair being visually and acoustically isolated from the other. One pair of ewes was exposed to the particular stress and the remaining pair acted as their own controls. The treatments were reversed 2 days later. In the second part of the experiment, 0, 0'01, 0'1,1'0 or 10·0 i.u. synthetic ACTH were injected as an intravenous bolus, after endogenous secretion had been suppressed by administration of synthetic glucocorticoid. All blood samples were taken via an indwelling jugular catheter. A comparison of cortisol release-estimated from a plot of cortisol in plasma versus time-following imposition of various stressor agents and administration of synthetic ACTH, allowed stress to be defined in terms of synthetic ACTH equivalents. The most severe stress was associated with shearing (0' 84 i. u. synthetic ACTH equivalents), less stress was imposed by yarding and handling (0'45 i.u.), and there appeared to be no effect attributable to feeding, fasting or oestrogen administration. The similarity in the pattern of cortisol release following ACTH administration offers the possibility of defining acute, but not chronic, stress in terms of ACTH equivalents.

Section: Discussionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Pattern of Cortisol Release in Sheep following Administration of Synthetic ACTH or Imposition of Various Stressor Agents

Fulkerson¹,

Jamieson²

1982

“…On these occasions jugular blood samples were collected into heparinized tubes. The samples were packed in ice until the plasma was separated by centrifugation within 2 h. The plasma was stored at -18°C until assayed for progesterone using the method of Bassett and Hinks (1969) as modified by Thorburn and Schneider (1972). The within and between assay coefficients of variation were less than 16 % over the range 1-8 ng progesterone.…”

Section: Determination 0/ Reproductive Functionmentioning

confidence: 99%

The Effect of 2-Deoxy-N-Glucose on Ovarian Function of Cattle

McClure¹,

Nancarrow²,

Hm³

1978

The administration of the metabolic inhibitor, 2-deoxY-D-glucose (2DG), to four well fed heifers just before and during the time of expected oestrus, and to another heifer following the removal of the corpus luteum, prevented both the occurrence of oestrus and the formation of corpora lutea in all animals. Plasma progesterone concentrations remained low for at least 10--21 days after the last dose of 2DG. The results suggest that the inhibition of glycolysis is associated with the failure of both oestrus and formation of functional corpora lutea, and· they support the hypothesis that hypoglycaemia is the primary biochemical change responsible for infertility induced by acute energy deficiency in lactating cattle.

“…The competitive protein binding (CPB) procedure used was essentially the same as that described by Thorburn et al (1969), employing light petroleum as the plasma extractant and dog or hen plasma as a source of corticosteroid binding globulin with [3Hzlcortisol as the competing tracer. Free and bound steroids were separated on small Sephadex G25 (fine) columns (Bassett and Hinks 1969).…”

Section: Hormone Assay Proceduresmentioning

confidence: 99%

“…Plasma corticoid concentrations were determined by the method of Bassett and Hinks (1969). Results expressed as cortisol equivalents (ng/ml) were corrected to allow for interference by progesterone present in the ethanol extract.…”

Section: Hormone Assay Proceduresmentioning

confidence: 99%

Hormone Studies on Ewes Grazing an Oestrogenic (Yarloop Clover) Pasture During the Reproductive Cycle

Obst¹,

Seamark²

1975

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 < 0·001) fertility.The first mating, when ewes were 1 t 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 < 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 < 0·05) within 8 h of birth. IntroductionReproductive difficulties in sheep grazing subterranean clover pastures were first described by Bennetts (1944) and Bennetts et al. (1946). Characteristic signs were ewe infertility, dystocia and uterine prolapse resulting in high ewe and lamb mortality. This syndrome of aberrant reproductive functions on clover pastures is now commonly referred to as 'clover disease' and its occurrence has been widely recognized in association with many different clover species throughout the world (Moule 1961;Moule et al. 1963;Bickoff 1968).The results of extensive studies have revealed that the aetiology relates to oestrogenic isoflavones present in the plants (Batterham et al. 1965). However, the exact way in which these substances exert their adverse effects on reproductive function is as yet unresolved. In the present study, an investigation has been carried out to examine the possibility that the clover acts by causing disturbances in the endocrinology of reproduction.Preliminary investigations (Obst et aT. 1971a) suggested that good indices of reproductive endocrine function for grazing flock sheep can be obtained by using relatively simple radio-ligand assays for plasma hormones. Comparison of these indices throughout the reproductive cycle was, therefore, made between a group of