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Biomedical subjects

G Peeters

Publications and source records attributed to G Peeters.

At least 55 records · Page 3Linked to original sources
PubMed1980

Effect of intracerebroventricular administration of opioid peptides on urinary function in the conscious goat.

The effects of methionine(met)-enkephalin, leucine(leu)-enkephalin, beta-endorphin and blocking substances upon renal function were studied in conscious goats. Injections were made through a permanent cannula into the 3rd ventricle. Leu- and met-enkaphalin, as well as beta-endorphin induced an antidiuretic response to the pituitary type. The responses to beta-endorphin were found to be dose-dependent. Pretreatment with naloxone, either into the 3rd ventricle or into the jugular vein, antagonised the antidiuretic responses to injected opioid peptides with the magnitude of the inhibition being dependent upon the dose. Atropine, hexamethonium or phentolamine did not interfere with the antidiuretic activity of beta-endorphin. Injection of naloxone alone into the 3rd ventricle of goats with a normal water balance, induced both a diuretic response and an increase in free water clearance. It is suggested that the opioid peptides are acting selectively on opiate receptors to influence the release of antidiuretic hormone.

Animals↗
PubMed1979

Metabolism of [U-14C; 2,3-3H]-L-valine by the isolated perfused goat udder.

Two lactating mammary glands excised from 2 goats were perfused for several hours in the presence of [U-14C; 2,3-3H]-L-valine and received adequate quantities of glucose, acetate and amino acids. In the synthesized milk 96 and 89% respectively of the casein valine was derived from free plasma valine. Valine was extensively catabolized by mammary tissue, resulting in a considerable 14CO2 production and in the incorporation of 14C into milk citric acid and to a lesser extent into casein aspartic acid and glutamic acid. About 30% of the valine molecules which were taken up by the mammary gland were oxidized to CO2 and 70% were incorporated in casein as valine residues. About 10% of the plasma valine molecules were reversibly transaminated during one passage through the udder. An important amount of radioactivity of plasma was present in unknown metabolites. Only 7% of this activity was localized in isobutyrate. The radioactivity of total milk fat was very low. Mainly iso-14:0, iso-16:0 and 15:0 were labelled.

Animals↗
PubMed1979

Metabolism of ornithine in perfused goat udder.

Four lactating goat mammary glands were perfused for several hours in the presence of ornithine labeled with 1-carbon-14 and delta-nitrogen-15 or 5-hydrogen-3 and received adequate quantities of glucose, acetate, and amino acids. For the first label carbon and nitrogen were incorporated in casein of milk. After isolation of the casein amino acids the carbon-14 was incorporated into proline only while nitrogen-15 was localized in aspartic acid, glutamic acid, alanine, serine, glycine, and the branched-chain amino acids. In the experiments with hydrogen-3 labeled ornithine, no reversible transamination of ornithine could be measured during passage through the udder. After incubation in vitro of goat blood in the presence of the labeled ornithine, no nitrogen-15 could be detected in other free amino acids of plasma. Ornithine is transaminated by the udder itself. The delta-amino group of ornithine contributed nitrogen for the synthesis of several nonessential amino acids in the mammary gland.

Amination↗
PubMed1979

Effect of intracerebroventricular administration of dopamine on urinary function in goats.

Dopamine (DA) and several blocking substances were administered into the 3rd ventricle of conscious goats to study the effects on water and electrolyte excretion. Intracerebroventricular infusion of DA in hydrated goats induced a significant dose-dependent inhibition of both the urine flow rate and the renal free water clearance. A biphasic response pattern of urinary electrolyte excretion, consisting of an initial fall, followed by an increase in the excretion rate was observed. The antidiuretic effects induced by DA could be prevented by prior administration of haloperidol, pimozide or phentolamine into the 3rd ventricle. Atropine, hexamethonium or propranolol were ineffective. It seems that excitatory responses of periventricular neurons resulting in vasopressin release in the goat may be mediated by both alpha-adrenoceptors and excitatory DA receptors. Furthermore, single injection of haloperidol or pimozide into the 3rd ventricle of goats with a normal water balance induced both a significant diuretic response and an increase in renal free water clearance. The data suggest that endogenous DA in the hypothalamus could be responsible for vasopressin release.

Animals↗
PubMed1977

Bovine serum growth hormone levels in clinical ketosis.

Blood samples were taken from ketotic cows and from normal lactating cows in summer and winter. The lowest serum growth hormone and plasma glucose levels and the highest serum free fatty acid values were observed in the ketotic cows. It is suggested that the decrease in growth hormone might benefit the ketotic animal.

Acidosis↗
PubMed1977

Nature of adrenoceptor sites in bovine teat muscles.

The motility of smooth muscles excised from the wall of bovine teats was studied "in vitro". These muscle preparations often show spontaneous rhythmic contractions. Administration of isoprenaline results in relaxation and decreased spontaneous motility, these effects being blocked by propranolol. Noradrenaline elicits contraction and stimulates rhythmical activity, these effects being inhibited by dibenamine. The effect of adrenaline is variable as it induces contraction or inhibition or biphasic responses. Dibenamine blocked contractions, whereas propranolol inhibited relaxations. It appears that alpha and beta adrenoceptors are present in teat muscles. Stimulation of the former elicits activation, whereas stimulation of the latter results in inhibition. These "in vitro" results are largely in agreement with "in vivo" responses described previously.

Animals↗
PubMed1977

Effect of prostaglandins F2alpha and E2 on milk ejection, blood pressure and blood flow through the mammary artery in the cow.

The influence of prostaglandins (PG) F2alpha and E2 on milk ejection, mammary artery blood flow and arterial blood pressure was studied in lactating cows. Injections of both PG in the jugular vein or the carotid artery induced milk ejection after a relatively long latency period. The minimal effective dose amounted to 1 to 5 microng and to 100 to 300 microng for PGF2alpha and PGE2 respectively. In several cases with PGF2alpha and once with PGE2 milk ejection was accompanied with a simultaneous increase in blood flow through the mammary artery whereas arterial blood pressure remained unchanged. Both routes of administration showed the same response. It was suggested that the effect of the PG on the bovine myoepithelium is indirect, possibly secondary to a release of oxytocin from the neurohypophysis.

Animals↗
PubMed1977

Mammary blood flow during experimental Escherichia coli endotoxin induced mastitis in goats and cows.

The effect of intramammary infusion of Escherichia coli endotoxin upon mammary blood flow was studied in lactating goats and cows. Blood flow was recorded by means of an electromagnetic flow probe chronically implanted around one mammary artery. Endotoxin mastatis was always accompanied by a significant increase in mammary blood flow, characterized by 2 conspicuous peaks. The flow returned to control values by the thirteenth hour after infusion. Other symptoms of acute mastitis were: fever, increased heart rate, swelling, heat and pain of the gland, increased chloride and total cell count in milk.

Animals↗
PubMed1977

Release of neurophysins I and II during and after parturition in cows.

Bovine neurophysin I and neurophysin II (bNpI and bNpII) have been assayed by radioimmunoassay in the jugular venous blood of cows during parturition. In general, low bNpI levels were detected on the day before labour began and during the first stage of labour. Neurophysin I was present in appreciable quantities in blood taken during the second stage of labour and in most cows the concentrations rose to a maximum during the expulsive stage. After delivery, the concentration of bNpI in the blood diminished. This pattern of release is similar to that reported for oxytocin at parturition in cows. As with bNpI, maximum levels of bNpII occurred during the expulsive stage of labour in some animals. In others, bNpII concentrations were very low or absent. Low concentrations of bNpII were found at the other stages of labour. Examination of the results from individual animals indicated that the release of the two neurophysins can be independent.

Animals↗
PubMed1977

Effect of prostaglandins F2alpha and E2 on milk ejection, blood pressure and mammary artery blood flow in the cow.

Injections of prostaglandins F2alpha (threshold dose: 1 to 5 microgram) and E2 (threshold dose: 1000 to 300 microgram) in the jugular vein or the carotid artery induced milk ejection in lactating cows after a relatively long latency period. In several cases with PGF2alpha and in one case with PGE2, milk ejection was accompanied by a simultaneous increase in blood flow through the mammary artery. Both routes of administration showed the same response. It is suggested that the effect of the prostaglandins on milk ejection is indirect, possibly secondary to a release of oxytocin from the neurohypophysis.

Animals↗
PubMed1976

Artificial induction of lactation by hypothalamic implantation of perphenazine in virgin goats.

Perphenazine (0-8-1 mg) caused udder growth and artificial induction of lactation, when stereotaxically implanted into the median eminence of virgin female goats. Sham implantations into the median eminence or implantation of perphenazine into sites of the hypothalamus not in the immediate proximity of the median eminence were ineffective. Fourteen-twenty-two d after implantation the goats were milked for the first time. Maximal milk yields of 250-1050 ml/d were achieved 3-5 months later. Udder development and induction of lactation during the premilking period were exclusively due to the action of perphenazine. It is likely that after implantation the milking stimulus played a synergic role with perphenazine in the progressive increase and the maintenance of lactation. Apparently no side effects were caused by the drug. Implantation of small doses of perphenazine in the hypothalamus might be a suitable technique for studying the physiological effects of increased levels of endogenous prolactin in goats.

Animals↗
PubMed1976

Influences of stress, age and sex on serum growth hormone and free fatty acid levels in cattle.

The serum growth hormone (BGH) and free fatty acid (FFA) concentrations of large groups of calves (male and female ranging in age from 8 to 14 days and from 3 to 6 months old), bulls, oxen, heifers and cows under normal conditions were compared with the serum BGH and FFA values of corresponding large groups of animals under stress conditions. Stress was caused by transport, as it routinely occurs, and was further reinforced by a stay of several hours in unfamiliar surroundings. Stress provokes a significant increase in serum FFA in all groups and induced a significant decrease in serum BGH in all groups, with the exception of the non-pregnant heifers. The male and female calves which were 8 to 14 days old, had significantly higher BGH levels than the older animals. The female calves from 3 to 6 months of age, and the heifers had significantly lower BGH levels than the cows. The males had higher serum BGH values than the females, but a significant difference could be demonstrated only between the male and female calves of both age-groups. The oxen, which were 1 to 3 years old, had significantly higher BGH levels than the non-pregnant heifers of the same age. It appeared that gestation had no influence on the serum BGH and FFA levels of both heifers and cows.

Age Factors↗
PubMed1976

Isolation of kallikrein from mammary gland of cows.

Small amounts of kallikrein were isolated from bovine mammary tissue. Immediately after slaughter, the udder was removed, perfused with ice-cold xylocaine-Rheomacrodex solution, and homogenized in ice-cold acetic acid solution. Kallikrein-like substances were adsorbed on DEAE-cellulose, eluted with ammonium formate and fractionated by acetone precipitation. The 40-70% acetone fraction was separated on a Shephadex-G 75 column and aliquots of each fraction were incubated for 1 or 2 hr with kininogen. After incubation, extracts were tested for kinin activity on the isolated rat uterus, the rat duodenum, blood flow through the femoral artery of dogs and by intramammary pressure assay in sheep. Release of kinins was demonstrated by all these techniques, highest kallikrein activity being detected in the molecular weight range 50,000 to 60,000. Direct injection of the enzyme into the udder artery of sheep, without prior incubation with kinninogen, resulted in vasodilation and a rise in intramammary pressure. The kallikrein activity was strongly inhibited by aprotinin, but not by soybean trypsin inhibitor or ovomucoid. Kallikrein activity was always associated with esterase activity.

Animals↗