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Biomedical subjects

J M Forbes

Publications and source records attributed to J M Forbes.

At least 91 records · Page 5Linked to original sources
PubMed1981

Evidence for hepatic glucostatic regulation of food intake in the domestic chicken and its interaction with gastro-intestinal control.

1. Male birds of a laying strain had permanent catheters introduced into the hepatic portal vein via the coccygeo-mesenteric vein. 2. Infusions of 5 ml of 40, 100 or 150 g glucose/l solution over 2 min caused a non-significant depression of food intake compared with a 9 g NaCl/l control solution. 3. Infusions of a range of isotonic glucose solution (0 to 60 g glucose/l, 30- mosm) at 1.4 ml/min over 3 h caused food intake depression within the 3-h period (P less than 0.01) proportional to the logarithm of the dose. 4. This effect was not observed when 60 g glucose/l was infused at the above rates into the jugular vein. 5. Starvation of the bird for 21 h accentuated the depressive effect of glucose load on food intake, especially when birds were not given food until after the 3-h infusion. 6. The infusion of solutions of sodium chloride (1.0 to 13.0 g/l, 33 to 433 mosmoles/kg) at 1.4 ml/min over 3 h stimulated food intake within the range of 3 to 7 g NaCl/l (100 to 233 mosm) but suppressed intake outside this range. This can be interpreted as a possible interaction with water intake control. 7. Infusion of 20 ml of glucose solution (0, 18 or 54 g/l) over 5 min into the crop and 0, 3.75 or 60 g glucose/l at 1.4 ml/min over 3 h into the hepatic portal vein, caused an additive, linear depression of food intake.

Animals↗
PubMed1981

Episodic growth hormone secretion in sheep in relation to time of feeding, spontaneous meals and short term fasting.

1. Blood samples were taken every 20 min (for at least 28 hr) from five castrate male and two anoestrus female and libitum fed sheep. Analysis for plasma growth hormone (GH) showed that two of the males, on two occasions, had regular, although individually specific, patterns of GH secretion (peaks 3.5-5 hr). The other animals all had irregular patterns of GH release. 2. Throughout the experiments, meal sizes and frequency were recorded and it was found that out of eighty spontaneous meals of at least 50 g, 57 (71%) occurred in the hour after GH peaks, which accounted for 50% of the total time. Furthermore, on twenty out of twenty-four occasions GH levels were found to be falling before the 'expected' feeding time when fresh food was offered and the animals normally consumed a large meal. The removal of the food from three of the males for 10 hr during an experiment prompted an increase both in the size and frequency of the GH peaks. After re-feeding, GH levels immediately fell and remained low for 1-2 hr. 3. We believe that these results show an association between GH secretion and meal feeding in sheep, and that GH secretion quickly responds to fasting. As GH levels fell before, or in the early stages of meals, this indicates a neural reflex in the inhibition of GH before a meal.

Animals↗
PubMed1981

Influence of boar contact on attainment of puberty in gilts after removal of the olfactory bulbs.

At 6-7 weeks of age the olfactory bulbs were removed from gilts which were then exposed to vasectomized boars for 30 min/day, starting on Day 160. Mean +/- s.e.m. age at first oestrus was similar in these gilts (230 +/- 15 days) to that in intact gilts not exposed to a boar (234 +/- 8 days) but greater (P < 0.05) than for sham- and un-operated gilts exposed to a boar (204 +/- 3 and 208 +/- 9 days, respectively). There were no differences in growth rate or ovulation rate at first oestrus. It is concluded that the main stimulus involved in the boar effect is olfactory in nature.

Animals↗
PubMed1980

Effects of insulin and gastro-intestinal hormones on feeding and plasma insulin levels in sheep.

Infusions of the following hormones were made into the hepatic vein of sheep over periods of three hours: pentagastrin (2.1, 5.0 or 9.9 micrograms/kg), pancreozymin (1.0 units/kg), secretin (2.0 units/kg), insulin (2.1 or 4.3 units/kg). Intake of the concentrate food was depressed by pentagastrin at 9.9 micrograms/kg/3 hr (P < 0.05) and increased by insulin at 4.3 units/kg/3 hr-(P < 0.05) Insulin levels in jugular plasma were unaffected by any of the gut hormone infusions. The liver is suggested as being involved in the control of food intake in sheep.

Animals↗
PubMed1980

Feeding in sheep during intraportal infusions of short-chain fatty acids and the effect of liver denervation.

1. Castrated male sheep were prepared with cannulae in the hepatic portal vein and jugular vein through which infusions lasting for 3 hr were made. Animals had free access to a pelleted feed the weight of which was continuously recorded so that feeding behaviour could be studied.2. Infusion into the portal vein of a mixture of salts of short-chain fatty acids (acetate, propionate, butyrate: 55, 30, 15) caused a dose-dependent depression in food intake, feeding stopping completely with 4.0 m-mole/min of the mixture. Jugular infusion depressed intake slightly, compared with controls.3. Separate infusions of salts of the three acids showed that the effect of the mixture was due almost entirely to its propionate content; 1.2 m-mole/min of propionate into the portal vein almost completely prevented feeding (39 g eaten per 3 hr) compared with jugular infusion at the same rate (210 g) or no infusion (205 g).4. Surgical sectioning of the hepatic nerve plexus around the wall of the hepatic artery was attempted. Of seven animals which recovered normal food intake, three continued to eat during portal vein infusions of propionate at 1.2 m-mole/min; these sheep were subsequently shown to have been at least 95% denervated. One animal was 50% denervated and ate normally during some infusions but not others. In the remaining three, feeding was suppressed by portal vein infusion of propionate, and these were less than 75% denervated.5. It was concluded that there are receptors in the liver which are sensitive to propionate and which have afferent fibres in the hepatic plexus.

Animals↗
PubMed1980

Diurnal variations of plasma prolactin in growing sheep under two lighting régimes and the effect of pinealectomy.

The role of the pineal gland in mediating the stimulatory effect of long daylength on blood levels of prolactin was investigated in 24 growing castrated sheep. Eight were pinealectomized, eight were sham-pinealectomized and eight remained as unoperated control animals. After a preliminary period with 12 h light : 12 h darkness (12L : 12D) pairs of similar sheep were allocated to photoperiods of 16L : 8D or 8L : 16D for 15 weeks. Each animal was individually fed at the same level as its partner exposed to the other daylength. Blood samples were taken weekly by jugular venepuncture. On two occasions, once in the preliminary period (12L : 12D) and again 41 days after the start of the subsequent photoperiods, samples were taken through indwelling jugular catheters at frequent intervals for 24 h. The plasma samples were assayed for prolactin by radioimmunoassay and concentrations were higher in samples taken by jugular puncture. There was a consistent positive effect of daylength on plasma prolactin in sheep with pineal glands that did not occur in pinealectomized sheep. In contrast, pinealectomy did not block the marked rise in prolactin that occurred at dusk. It appears that the effect of the photoperiod on levels of plasma prolactin throughout the day and night is not mediated by the same mechanism as that which controls the surge of prolactin at dusk in the sheep.

Animals↗
PubMed1980

Somatomedin-like activity in cattle: the effect of breed, lactation and time of day.

Somatomedin-like activity (SLA) was measured in plasma samples from cattle using the porcine costal cartilage disk bioassay. In 40-day-old pre-ruminant bull calves, SLA was highest in the plasma of eight Friesians (mean potency 0.97 +/- 0.06 (S.E.M.) units/ml), lowest in five Aberdeen Angus x Friesians (0.78 +/- P < 0.05) and intermediate in six Hereford x Friesians (9.89 +/- 0.09). Plasma levels of SLA were significantly (P < 0.01) lower in eight lactating Friesian (high-yielding) cows (0.53 +/- 0.04) than in five dry cows (0.76 +/- 0.06). Levels of SLA in the plasma of a further eight lactating Hereford x Friesian (low-yielding) cows (0.76 +/- 0.07) were similar to the levels in the plasma of the five dry dairy cows. Large diurnal changes in plasma SLA occurred in lactating Hereford x Friesian and Friesian heifers. In three Hereford x Friesian heifers plasma levels of SLA were lowest at 19.00 h (0.39 +/- 0.07) and highest at 03.00 h (0.77 +/- 0.08). A similar pattern was present in plasma samples from three Friesian heifers; the lowest levels of SLA being at 21.00 h (0.37 +/- 0.07) and the highest at 05.00 h (0.61 +/- 0.13). Throughout the period of 24 h the overall mean levels of SLA were significantly (P < 0.01) higher in the plasma samples from the three Hereford x Friesian heifers (0.6 +/- 0.01) than in the samples from the three Friesian heifers (0.49 +/- 0.02 units/ml).

Animals↗
PubMed1979

Hormones, feeding and temperature in sheep following cerebroventricular injections of neurotransmitters and carbachol.

1. The neural mechanisms involved in the control of prolactin and growth hormone secretion, body temperature and feeding in castrated male sheep were investigated by the lateral cerebroventricular injection of several putative neurotransmitters and carbachol. 2. Feeding was inhibited by 10 and 20 microgram carbachol and by 400 microgram histamine. 100 microgram Noradrenaline stimulated, but 200 microgram inhibited, feeding; however, both results were non-significant compared with controls. 3. 20 microgram Carbachol elicited a highly significant rise in plasma growth hormone, suggesting a cholinergic component in the neural control of growth hormone in sheep. Noradrenaline, dopamine and 5-hydroxytryptamine, but not melatonin, significantly depressed plasma prolactin concentration indicating a similar neural control for the hormone's release in sheep as in other species. 4. Deep body temperature appeared unaffected by any ofthe injected drugs. 5. The possible interrelationships between feeding behaviour and the circulating levels of growth hormone in ruminants is discussed. 6. A method for the radioimmunoassay of ovine growth hormone is described and validated.

Animals↗
PubMed1979

Somatomedin-like activity in plasma after foetal hypophysectomy or nephrectomy and in experimental intra-uterine growth retardation in sheep.

Plasma samples from pregnant ewes and their foetuses during the last quarter of gestation were assayed for somatomedin-like activity (SLA) using the procine costal cartilage assay. In maternal plasma, the mean potency (compared with pooled serum from six sheep) was 0.84 +/- 0.05 (S.E.M.) units/ml (n = 15). Somatomedin-like activity in the plasma of five control foetuses (0.91 +/- 0.1 units/ml) was similar to the maternal levels and did not change with gestational age. After foetal hypophysectomy the SLA in foetal plasma (0.37 +/- 0.05 units/ml, n = 4) was significantly less than in control animals. In two nephrectomized foetuses, the mean SLA in plasma (0.08 and 0.51 units/ml respectively) was less than in control animals. Retardation of intra-uterine foetal growth was induced by removal of endometrial caruncles before pregnancy in four sheep. The SLA in plasma from these foetuses was 0.38 +/- 0.05 units/ml (P less than 0.01 v. control animals). The results suggest that SLA in the foetus may be important in the regulation of foetal growth, but they also indicate that factors other than growth hormone may be important in the control of SLA in foetal plasma.

Animals↗
PubMed1979

Changes in somatomedin-like activity and concentrations of growth hormone and prolactin in the plasma of castrated growing lambs.

Somatomedin-like activity was measured in the plasma of growing lambs using the porcine costal cartilage disk assay. Plasma concentrations were found to be high initially at 2 days of age (mean potency 1.02 plus or minus 0.13 (SEM) units/ml, n = 4) declined significantly by 8 days of age (mean potency 0.65 plus or minus 0.04 units/ml, n = 5, P less than 0.01, analysis of variance). Thereafter somatomedin-like activity declined slowly to reach its lowest concentration at 146 days of age (mean potency 0.61 plus or minus 0.04 units/ml, n = 5) then it rose slowly until 288 days of age (mean potency 0.61 +/- 0.04 units/ml, n = 5. These changes in somatomedin-like activity were accompanied by high initial plasma concentrations of growth hormone (24.8 plus or minus 4.8 ng/ml, n = 5) which declined under 188 days of age (2.8 plus or minus 0.04 ng/ml, n- 5) and then rose slightly until 288 days of age (13.8 plus or minus 9 ng/ml, n=5). Plasma prolactin concentrations showed a different pattern being low initially (47.8 plus or minus 8.7 ng/ml, n = 5) rising until 146 days of age (203 plus or minus 16 ng/ml, n = 5) and then declining to low value for the rest of the experiment. The relationships between these factors is not clear but somatomedin-like activity shows a pattern in the lamb which is highest when growth is faster (i.e. in the young lamb).

Animals↗