Plasma renin activity during controlled hemorrhage in the dog.

Purebred 1-year-old Beagles were made hypotensive by controlled hemorrhage (3 ml/kg-1/min-1). Femoral artery blood samples were collected every 5 minutes during controlled hemorrhage, until the blood pressure decreased to 30+/-5 mm Hg. Samples were then collected every 10 minutes for 40 minutes. Blood was not reinfused during the procedure. Carotid blood pressure, electrocardiogram lead II, and respiration rate were recorded. The results of the radioimmunoassay for renin activity indicated that arterial plasma renin activity formed a bimodal activity curve. Plasma renin activity did not reach any plateau, and it continued to increase throughout the experiment. Decreasing blood pressure and heart rate statistically showed a relationship with plasma renin activity (P less than 0.001). There was no interaction between pressure and heart rate; both were strong and independent. Female dogs had a higher plasma renin activity than did male dogs (P less than 0.001) throughout the experimental period. Plasma renin activity remained above resting activity throughout the development of hemorrhagic shock.

Effects of acetate on absorption of solute and water from the pig colon.

The effect of acetate, at physiologic concentrations, on sodium and water absorption in the temporarily isolated colon of the conscious pig was studied with isotonic perfusion solutions buffered at pH 6.4 or 7.4, in which either chloride or acetate was present as the major anion. Sodium and water absorption was greater from the acetate solution when the pH was low; however, acetate reduced sodium and water absorption below that observed with the chloride solution when the pH was high. There were no significant differences observed in sodium or water absorption from the chloride solution at either pH. We conclude that the concentration of undissociated acetate influences sodium and water absorption in the colon of the pig. Such an effect may have important consequences on the reserve absorptive capacity of the colon in certain diarrheal diseases.

Lactate as a precursor of fatty acids in bovine adipose tissue.

In vitro experiments were conducted to determine the rates of lactate, acetate, and glucose conversions to glycerol, CO2, and fatty acids by subcutaneous adipose tissue of cattle. To study the pathway for lactate utilization as a carbon source for lipogenesis, the effect of each of four substates (lactate, acetate, pyruvate, and glucose) on the rate of conversion of the other three was determined. The rates of lactate conversion to fatty acids and to glycerol were greater than those for acetate and glucose. Acetate, however, was oxidized to CO2 at greater rates than either lactate or glucose. Acetate was used for fatty acid synthesis at greater rates than pyruvate was less than that from lactate but greater than that from glucose. Acetate additions to the incubation media decreased the synthetic rates from lactate, pyruvate, and glucose. Pyruvate decreased rates of fatty acid synthesis from glucose but slightly (not statistically significant) stimulated synthesis from lactate and acetate. Lactate decreased glucose and pyruvate utilization but had no effect upon that of acetate. Our results clearly demonstrated that lactate can be used for fatty acid synthesis as well as for glycerogenesis by bovine adipose tissue.

Further evidence to support the alpha 2-adrenergic nature of amitraz-induced decrease in intestinal motility.

The effect of amitraz, a formamidine insecticide, on in vitro intestinal contractions was studied in teh transmurally-stimulated guinea-pig ileum. An electrical stimulation (with 80 V/0.5 msec/0.1 Hz shown on the dial of the stimulator) caused the ileum to contract presumably via the release of acetylcholine. Amitraz (10(-7) to 10(-6) M) produced a dose-dependent inhibition of these transmurally-stimulated contractions. This effect of amitraz was blocked and reversed by idazoxan (10(-6) M), an alpha 2-adrenoceptor antagonist, but was not prevented by prazosin (10(-6) M), an alpha 1-adrenoceptor antagonist. These results suggest that alpha 2-adrenoceptors mediate the effects of amitraz on the transmurally-stimulated guinea-pig ileum. The results also suggest that amitraz decreases intestinal contraction by activating the alpha 2-adrenoceptors in the myenteric (Auerbach's) plexus, thus inhibiting parasympathetic tone.