The effect of a 72-h fast on plasma levels of pituitary, adrenal, thyroid, pancreatic and gastrointestinal hormones in healthy men and women.

Seventeen human subjects fasted without electrolyte replacement for 3 days and hormone levels were measured before, during and after the fast. Immediate consequences of the fasting state in healthy human subjects include a marked increase in plasma cortisol. ACTH, beta-endorphin, beta-lipotrophic hormone, adrenaline, noradrenaline and dopamine. Levels of all these hormones were much greater on the first morning of the fast than in the post-prandial state, even though the plasma glucose level was no lower than that observed on the morning before the fast began. A clear fall in TSH and tri-iodothyronine (T3) levels was observed, but thyroxine levels did not change significantly. Insulin levels fell whereas proinsulin levels did not fall during the fast, though they did rise markedly upon re-feeding. An increase in GH levels was particularly apparent in male subjects, but was also seen in females when evening samples were compared. Pancreatic glucagon showed a modest rise during the fast, but fell again on refeeding; total glucagon also rose as the fast proceeded, but increased markedly upon re-feeding. Levels of gastrin and peptide YY remained low during the fast. Plasma electrolyte levels were unchanged. The following were closely correlated: cortisol with ACTH, T3 with log10 TSH, dopamine with noradrenaline, and (negatively, during the fast) pancreatic glucagon with glucose.

Release of neuropeptide Y in response to splanchnic nerve stimulation in the conscious calf.

Plasma concentrations of neuropeptide Y were determined by means of a specific radioimmunoassay in the conscious calf. Significantly higher concentrations were found in the adrenal venous effluent (102 +/- 34 pmol/l) compared to systemic arterial plasma (11 +/- 7 pmol/l). Stimulation of the splanchnic nerves at 40 Hz in bursts for 1 s at 10 s intervals resulted in a slow sustained rise in plasma neuropeptide Y in both adrenal (peak 1124 +/- 217 pmol/l and peripheral (peak 771 +/- 182 pmol/l) samples. Experiments performed in adrenalectomized calves produced a closely similar release of neuropeptide Y when the nerves were stimulated intermittently in the same pattern and under the same conditions. Stimulation of the splanchnic nerves at 4 Hz continuously resulted in a smaller response. Pre-treatment with hexamethonium completely abolished the rise in plasma neuropeptide Y concentrations.

Neuropeptide Y (NPY) reduces myocardial perfusion and inhibits the force of contraction of the isolated perfused rabbit heart.

Isolated rabbit hearts, perfused under constant pressure (Langendorff technique) were used to study the effect of neuropeptide Y (NPY) on heart rate, force of heart contraction and rate of myocardial perfusion. No significant net change in heart rate was noted. A dose-dependent negative inotropic effect was consistently demonstrated which was characterised by slow onset and was often preceded by a transient positive inotropic response. Addition of small doses of NPY resulted in a prompt reduction in flow of the perfusate through the coronary vasculature. Since NPY is present locally in cardiac nerves, these effects may have physiological importance.