Celiac Blood Flow Regulation, Acid-Base Balance and Production in Heat-Stressed Cockerels (Cate Cholamines)

[摘要] An acid-base disturbance characterized by reduced blood CO2 and H+ content developes in heat-stressed panting fowl. An acid-base imbalance could reduce productivity either by reducing metabolic efficiency or by depresing energy absorption by reducing gastrointestinal blood flow.Growth trails were performed to determine the effect of carbonated water (CW) on performance of heat-stressed cockerels. Compared to birds provided tap water (TW), CW improved average daily gain or feed efficiency in cockerels subjected to constant 33 C or to cyclic 29-34 C temmperatures, respectively. Cockerels infused with CW directly into the crop exhibited higher blood PCO2 and lower blood pH compared to TW infused cockerels after 90 min of heat stress.Next, studies were designed to elucidate the physiological basis of heat-induced celiac mean blood flow (MBF) reduction in fed cockerels chronically instrumented with electromagnetic blood flow probes. Heat stress reduced MBF by 50% compared to thermoneutral control values. MBF changes were highly correlated (-.83 to -.89) with celiac vascular resistance (CVR), but poorly correlated with blood PCO2 and pH. The nearly complete abolition of heat-induced celiac vasoconstriction by prior infusion of phenoxybenzamine clearly demonstrated sympathetic regulation of MBF during heat stress. Plasma samples obtained during heat stress were analyzed for epinephrine (E), norepinephrine (NE), and Dopamine (DA). Heat stress initially reduced E and NE and increased DA titer. NE remained depressed throughout heat stress but increasing E titer during the heat stress period was concomitant with increasing heart rate and rectal temperature. Contrary to accepted NE activity on intestinal smooth muscle vasculature, plasma NE was directly correlated (.93) with MBF and inversely correlated (-.96) with CVR.From these studies it was concluded that:(1) Heat-induced MBF reduction was due to sympathetic regulation, independent of blood PCO2 or pH changes. (2) Heat-induced celiac vasoconstriction was apparently due to local sympathetic release of catecholamines and not from changes in plasma catecholamine concentrations. (3) CW may increase growth or feed utilization by partially ameliorating the acid-base imbalance associated with heat stress.

[关键词] Biology, Animal Physiology