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Biomedical subjects

G Peeters

Publications and source records attributed to G Peeters.

At least 37 records · Page 2Linked to original sources
PubMed1983

Release of neurophysin I and oxytocin by stimulation of the genital organs in bulls.

Oxytocin and bovine neurophysin I (bNpI) were estimated by radioimmunoassay in jugular vein plasma which was collected continuously from 18 bulls. No release of peptides was observed during successive matings with a cow in oestrus or during successive mountings on a cow with ejaculations into an artificial vagina. Stimulation with an electro-ejaculator or, to a smaller extent, massage of the seminal vesicles and ampullae per rectum caused an increase of oxytocin accompanied by a release of bNpI. It is speculated that the release of these peptides is due to stimulation of afferent pelvic nerves in the rectal wall. Basal molar ratios of bNpI/oxytocin in the plasma were highly variable, often showing a large excess of either bNpI or oxytocin. After the onset of peptide release induced by stimulation, molar ratios approached 1:1. This might indicate that hormone release is by exocytosis. Basal bNpI does not provide a good reflection of the oxytocin level.

Animals↗
PubMed1983

Propionate for fatty acid synthesis by the mammary gland of the lactating goat.

Isolated mammary glands of lactating goats were perfused with heparinized and oxygenated blood for 8 to 15 h. Adequate quantities of glucose, acetate, and amino acid were added to the perfusate. After addition of propionate to the perfusion blood, concentrations of odd-numbered and of monomethyl-substituted fatty acids other than those with iso and anteiso configuration increased in the milk fat. These acids seem to be synthesized de novo in the mammary gland. The increase of C17:0 concentration was weak and problematic. We suggest that propionate is acting as a precursor for monomethyl-substituted fatty acids by way of methylmalonyl-CoA. The activating effect of propionate administration upon milk fatty acid production was largest for odd-numbered followed by monomethyl-substituted fatty acids. No increase of iso acids was observed in milk fat in the propionate-infused glands whereas the increase of anteiso acids was extremely small. This agrees with the conception that iso and anteiso fatty acids are synthesized by rumen bacteria.

Animals↗
PubMed1982

Effect of hypothalamic implantation of perphenazine on milk yield in goats.

The effects of perphenazine on galactopoiesis were studied in 52 goats in the phase of declining lactation (September-December). At the beginning of September, perphenazine (1 mg) was stereotaxically implanted into the hypothalamus, sham-implantations being performed on control animals. After the operation milk yield decreased and stabilized at a new starting level in most animals of both groups. The average weekly milk yield of the sham-implanted goats gradually fell during the experimental period. This progressive decline in yield was greatly reduced if perphenazine had been implanted in the median eminence (ME). No galactopoietic effects were observed when the implantation was localized outside the ME.

Animals↗
PubMed1982

Effect of prostaglandin synthetase inhibitors on mammary blood flow during experimentally induced mastitis in lactating goats.

Mammary blood flow (MBF) was recorded chronically in lactating goats by means of an electromagnetic flow probe. Experimental mastitis was induced by intramammary injection of E. coli lipopolysaccharides. Control mastitis experiments were accompanied by a significant increase in MBF characterized by 2 conspicuous peaks, by fever, increased heart rate, swelling, heat and pain of the gland, and increased chloride in milk. The non-steroidal anti-inflammatory drugs suprofen, indomethacine and flurbiprofen were potent antipyretics during mastitis but had only little effect on the biphasic MBF pattern. Indomethacine induced a strong and long lasting vasoconstriction in the udder. MBF peak I was quantitatively unaffected although flurbiprofen was able to delay its appearance. All drugs partially suppressed MBF peak II, this being most significantly with flurbiprofen. None of them prevented either swelling of the gland or high milk chloride but all inhibited pain in the gland. MBF peak II may be partially induced by the decrement stage of fever. Locally formed prostaglandins play little or no role in the genesis of MBF peak I but may be involved in MBF peak II.

Animals↗
PubMed1982

Effect of experimentally induced fever on mammary blood flow in lactating goats.

The effect of artificially induced fever on normal mammary blood flow (MBF) was studied in conscious lactating goats in a thermoneutral environment. Fever was induced either by intravenous (i.v.) injection of LPS or by intracerebroventricular (i.c.v.) infusion of PGE2. The increment stage of fever was always accompanied by a fall in MBF, shivers and miosis. There was a positive correlation between the intensity of temperature increase and MBF decrease. Once fever was established or during the decrement stage of fever, MBF returned to control levels and often increased far above pre-injection values. These specific circulatory changes observed in the lactating udder of the goat might contribute to the genesis and lysis of fever. MBF might play an important role in the pathogenesis of fever in the lactating goat. The effect of centrally induced fever was studied on the biphasic MBF pattern normally occurring during experimentally induced LPS mastitis. PGE2 was infused i.c.v. practically simultaneously with the intramammary administration of LPS. In most experiments fever occurred earlier than during control mastitis. The biphasic MBF-curve was strongly altered, MBF peak I being inhibited. Fever increment during control mastitis could be one of the factors limiting the duration of MBF peak I and fever decrement could induce peak II.

Animals↗
PubMed1981

Effect of atropine on plasma amino acid levels and milk secretion of cows.

Subcutaneous injections of 30 mg atropine into lactating cows induced a 20--40% decrease of free amino acid (AA) levels in arterial plasma. Minimum levels were observed after 30--50 min. The decline persisted for more than 6 h. The greatest fall in concentration was noted for tyrosine, methionine, lysine, arginine, phenylalanine and threonine. Arterial glucose levels remained unaffected. The effect of atropine on milk secretion was studied in 2 cows which were milked every hour with the aid of oxytocin. Maximal effects were observed after 3--4 h. They included reduction in concentration of casein and alpha-lactalbumin (alpha-la) and a decline in production of milk (20%), casein (35%), alpha-la (45%) and lactose (18%). Uptake by the lactating udder over a period of about 1 h after injection of atropine was studied in 2 cows. Mammary blood flow and glucose uptake remained unaffected. There was a positive correlation between arteriovenous differences of essential AA and arterial plasma concentrations. The uptake of essential AA decreased by approximately 50%. There was no evidence that atropine has a direct inhibiting effect on the udder. It is suggested that the decrease of alpha-la synthesis might induce an inhibition of lactose synthesis and milk production.

Amino Acids↗
PubMed1980

Studies on the motility of smooth muscles of the teats in lactating cows.

Rhythmic motility of teats in lactating cows in vivo was studied by an improved plethysmographic technique. Oxytocin was infused intravenously and drugs were injected into the artery of the filled udder. The beta-adrenergic agent, isoprenaline, induced relaxation of the teats whereas the alpha-adrenergic agents phenylephrine and noradrenaline, elicited contraction. In one animal however, noradrenaline always exerted a biphasic effect. Pre-treatment with propranolol, a beta-adrenergic blocking agent, changed the biphasic effect into a purely activating response. Adrenaline, which exhibits both alpha and beta effects, induced relaxation, but after propranolol treatment relaxation was abolished and even converted into contraction of the teat. It seems clear that both alpha and beta adrenoceptors are present in longitudinal smooth muscles of the teats. Milk losses as intermittent spurts were observed in several cows. Spurts occurred synchronously with rhythmical teat motility in the filled udder during oxytocin infusion. The intensity of milk leakage was increased by isoprenaline and inhibited by noradrenaline, indicating the presence of alpha and beta receptors in teat sphincter muscles. Starting and stopping of milk spurts in correlation with rhythmical teat contractions were studied by audiovisual synchronization of video recording tape. The most common type of spurt began near the middle of the teat's relaxation phase and ended either just before or exactly at the beginning of the contraction phase. Interruption of the spurt is primarily due to closure of the streak canal.

Animals↗