The effects of the muscarinic agonist oxotremorine-m (Oxo-m) on 45Ca and 86Rb fluxes, insulin secretion, cytoplasmic Ca2+ concentration ([Ca2+]i) and membrane potential in pancreatic B-cells were studied. Oxo-m (40-200 μM) increased the [Ca2+]i by about 250 nM, irrespective of the glucose concentration present in the medium (2·8-22 mM). This effect was reduced by 50 % upon the addition of EGTA. Oxo-m (50 μM) increased the 45Ca efflux from islets perifused in the absence or presence of [Ca2+]o, although under the former condition this efflux was transient. The difference between effluxes measured in the absence and presence of [Ca2+]o represents the sustained second component, which presumably reflects Ca2+ influx. In both the absence and presence of 11·2 mM glucose, Oxo-m (50 μM) transiently increased 86Rb efflux. In the presence of glucose, Oxo-m provoked a transient polarization of the B-cell membrane associated with an increase in the K+ permeability values. K+ permeability returned to basal values (no Oxo-m) after 1-2 min. These results indicate that the initial phase of Oxo-m-induced insulin secretion depends partially on intracellular Ca2+ release, and that the sustained enhancement of release depends on Ca2+ influx. The participation of a calcium release-activated current (ICRAC) is proposed to explain the sustained small changes in membrane potential.

The enzymic activity and immunoreactivity of rat tissue kallikrein (rK1) secreted at rest by granular duct cells of unstimulated submandibular glands has been compared with that secreted on autonomic nerve stimulation. Although a direct vesicular, constitutive secretory pathway operates for rK1 secretion from granular duct cells of unstimulated and parasympathetically stimulated glands the rK1 was not present in a pro-form and actually showed a greater enzymic activity per unit immunoreactive protein than the granule-derived rK1 in sympathetically evoked saliva. Constitutively secreted rK1 was found to be in a single chain molecular form by reducing SDS gel electrophoresis. In contrast rK1 secreted from the storage granule pool of granular duct cells on sympathetic nerve stimulation was present in much higher amounts and occurred in both one-chain and two-chain forms as revealed by SDS gel electrophoresis under reducing conditions. The lower enzymic potential of rK1 in sympathetically evoked saliva might be accounted for by its conversion to a two-chain form.

The contractile regulation of neonatal smooth muscle was studied in rat neonatal portal vein. Strips of β-escin-permeabilized portal vein from 3- to 5-day-old rats and 5- to 6-week-old rats were mounted on a 'bubble chamber' in calcium solutions buffered with 10 mM EGTA. Although the overall tension development was lower in neonatal muscle as expected, the calcium sensitivity of the neonatal permeabilized portal vein was significantly higher than in developed portal vein. Endothelin-1-induced sensitization of the myofilaments was investigated. Endothelin-1 produced an increase in tension of permeabilized neonatal portal vein in a calcium solution buffered with 10 mM EGTA. This sensitization was proportionally higher in neonatal than in developed smooth muscle, despite similar initial submaximal calcium contractions. GTPγS-induced calcium sensitization was also proportionally higher in neonatal permeabilized strips than in fully developed smooth muscle. These changes may be due to alterations in the intracellular signalling pathways which mediate calcium sensitization in smooth muscle. As some endothelin-1-mediated responses are known to occur via activation of the heterotrimeric GTP-binding protein, Gq, the levels of protein expression of Gqα were studied. In membrane preparations from neonatal rat portal vein the expression of Gqα was significantly higher than in portal vein membrane preparations loaded with equal protein from 5- to 6-week-old rats. In conclusion, agonist-induced sensitization of the myofilaments was higher in neonatal rat portal vein than in fully developed portal vein. This difference is the result of changes in intracellular signalling and may be partly produced by the greater expression of Gqα observed in neonatal portal vein.

The existence of abdominal arterial baroreceptors has long been controversial. Previously difficulties have been encountered in localizing a stimulus to abdominal arteries without affecting reflexogenic areas elsewhere. In these experiments, using anaesthetized dogs, the abdomen was vascularly isolated at the level of the diaphragm, perfused through the aorta, and drained from the inferior vena cava to a reservoir. Changes in abdominal arterial pressure were effected by changing the perfusion pump speed. During this procedure the flow back to the animal from the venous outflow reservoir was held constant. Increases and decreases in abdominal arterial pressure resulted, respectively, in decreases and increases in perfusion pressure to a vascularly isolated hind-limb and in some dogs also a forelimb. Responses were significantly larger when carotid sinus pressure was high (120-180 mmHg) than when it was low (60 mmHg). Responses were still obtained after cutting vagus, phrenic and splanchnic nerves, but were abolished by spinal cord lesion at T12. These experiments provide evidence for the existence of abdominal arterial baroreceptors. The afferent pathway for the reflex vasodilatation appears to run in the spinal cord.

The effects on renal functions of infusing glucagon (100 ng kg-1 min-1) into the portal vein system were studied in young anaesthetized sheep kept on a diet with normal protein and digestible energy contents. The clearance measurements of the left kidney functions showed a decreased urine flow rate (from 0·36 ± 0·04 to 0·18 ± 0·03 ml min-1; P < 0·01) within the first 10 min of glucagon infusion, falling to 0·07 ± 0·02 ml min-1 (P < 0·01) during the next 10 min. The glomerular filtration rate also decreased from 17·56 ± 2·92 ml min-1 to its lowest value, 3·34 ± 1·02 ml min-1, (P < 0·01) after 20 min of glucagon infusion. Decreases in urea excretion (from 53·1 ± 6·46 to 3·82 ± 1·27 μmol min-1; P < 0·01) and osmotic clearance (from 0·67 ± 0·13 to 0·09 ± 0·02 ml min-1; P < 0·01) occurred during the first 20 min. The plasma level of glucose increased from 4·01 ± 0·53 to 8·33 ± 1·12 mmol l-1 (P < 0·05) 20 min after the start of glucagon infusion. Twenty minutes after the start of glucagon infusion, the values of all the parameters measured began to recover, although they did not reach the control level, even after 1 h. Blood pressure was stable during the whole experiment. The results show that the effects of intraportally infused glucagon on kidney functions in sheep are the opposite of those obtained from similar experiments in laboratory animals with simple stomachs or in humans.

This study examines the precise time course that brown adipose tissue (BAT) takes to adopt the characteristics of white adipose tissue in postnatal lambs. Perirenal adipose tissue was sampled from ewe-reared lambs within 1 h of birth and at 1, 2, 4, 7, 14, 21 and 30 days of age and analysed for the amount of mRNA for uncoupling protein (UCP), the amount and activity of UCP, and protein, mitochondrial protein and lipid content. This was combined with measurements of colonic temperature and jugular venous plasma concentrations of thyroid hormones and insulin-like growth factor-1 (IGF-1). Over the first 4-7 days of age, large quantities of UCP mRNA were associated with a peak in plasma triiodothyronine concentration at 2 days of age followed by a maximal amount and activity of UCP at 4 days and a basal colonic temperature of 39·3°C. Between 7 and 30 days there was a large increase in lipid deposition as the amount and activity of UCP and the amount of UCP mRNA declined to basal values and colonic temperature was maintained at 40°C. A significant positive relationship between perirenal adipose tissue lipid content and plasma IGF-1 concentration was observed throughout the study period. It is concluded that ovine adipose tissue maturation occurs in two distinct phases over the first month of life. The precise time scale of this process could be regulated in part by the lamb's body temperature which determines whether adipose tissue is required for heat production (i.e. BAT) or as an endogenous energy source (i.e. white adipose tissue).

Feeding a high-carbohydrate (CHO) diet and administration of alkalinizing agents have both been shown to improve performance in high-intensity exercise. The effect of these treatments in combination was investigated in the present study. Six healthy male subjects exercised to exhaustion on an electrically braked cycle ergometer at a power output equivalent to 100 % of their maximum oxygen uptake (VO2,max) on four separate occasions. Each subject consumed either a diet with the same composition as his normal diet (termed the experimental normal (N) diet; 54 ± 7 % CHO, 13 ± 2 % protein, 33 ± 7 % fat) or a high-CHO diet (81 ± 2 % CHO, 13 ± 2 % protein, 6 ± 1 % fat) that had the same energy and protein content for the 3 days prior to the exercise tests. Subjects then ingested either a placebo (CaCO3) or trisodium citrate (0·3 g (kg body mass)-1) 3 h before exercise. Time to fatigue was not different between experimental conditions. Consumption of the high-CHO diet had no effect on blood acid-base status, but the ingestion of sodium citrate induced a mild metabolic alkalosis after both the N diet and the high-CHO diet. This alkalinizing effect was also evident after exercise, since blood pH, plasma bicarbonate and blood base excess were higher (P < 0·05) after the ingestion of sodium citrate than under the placebo conditions. The changes in blood lactate, pyruvate and glucose and plasma glycerol after exercise were similar for all experimental conditions. Blood lactate, glucose and pyruvate and plasma glycerol concentrations increased from resting values (P < 0·01) following exercise but this increase was similar under all experimental conditions. These data demonstrate that when the energy and protein content of the diets is the same, exercise capacity and the metabolic response to intense exercise are similar following consumption either of a high-CHO diet or a more normal diet. Acute ingestion of sodium citrate prior to exercise resulted in a reduction in post-exercise acidosis despite a blood lactate concentration that was similar to that observed after the ingestion of a placebo, but did not affect exercise performance under the conditions of this study.