P. C. Harrison

Scotophase-Dependent Thermoregulatory Dysfunction in Pinealectomized Chickens:

Summary Pinealectomized female chickens (PX) were given an acute thermal challenge (60 min at 42°) during two portions of their 12L:12D photoperiod. Five birds from each surgical treatment group, including sham operated (PN) and nonoperated controls (C), were exposed to heat 4 hr after onset of light (photophase) and a like number 4 hr after onset of darkness (scoto-phase). There were no differences in rectal temperature (TT) or respiratory rate (RR) among treatment groups of the photophase heat challenge. Heat exposure during the scotophase caused a significantly greater (P < 0.01) hyperthermia in PX birds after 20 min of heat. At the conclusion of the nocturnal challenge, PX birds had a T r 1.0° higher than PN and C birds. Time-of-day comparisons of RR showed a significant (P < 0.05) interaction between pinealectomy and time-of-day at 30 min of exposure; the RR of PX birds was lower at night. The authors thank Dr. H. W. Norton for statistical analysis of these data.

Temperature Preferendum of Pinealectomized Cockerels during Their Light-Dark Cycle

Summary Pinealectomized cockerels (PX) were individually exposed to a thermocline (20 to 34°) throughout both phases of the light-dark cycle (12L:12D). Twelve birds from each surgical treatment, including sham operated (PN) and unoperated controls (C), were singly placed in the thermocline for 100 min during photophase and scotophase in 4-hr segments designated early (E), middle (M), and late (L). Prior to placement in the thermocline, PX birds had a lower mean T r (40.15°) than PN and C groups (40.64°). During photophase, PX birds selected a higher T a during the E and L segments, but preferred a T a similar to PN and C cockerels for M photophase (23°). This produced an interaction (P < 0.05) between pinealectomy and T a selection during photophase. The PX group had a T a preferendum of 29.7° for scotophase in contrast (P < 0.05) to 25.4° selected by PN and C birds. The average T a preferred by PX birds across both phases of the light-dark cycle was 28° (P < 0.05) while on the average, PN and C groups selected 24°.

Reversal of depressed miduterine arterial flow during hyperthermia-induced respiratory alkalosis.

Abstract The influence of ambient and arterial PCO2 on miduterine arterial flow of pregnant sheep acutely exposed to hot environments was investigated. Five mixed-breed ewes between 120 and 130 days of gestation were subjected to hot environments (increasing from thermoneutral 23 to 40°C), and arterial blood pH, PCO2, and PO2 were determined at 5-min intervals. Respiratory rate, heart rate, rectal temperature, blood pressure, and miduterine arterial flow were continuously monitored prior to and during elevation of ambient air temperature. When miduterine arterial flow had decreased to 50% of thermoneutral control levels, ambient air CO2 was increased to 2.5%. Elevated ambient inspired CO2 caused a reversal in arterial pH and PCO2 to near thermoneutral levels. Miduterine arterial flow increased to 77% of the control levels following the elevated ambient PCO2 period. Respiratory rate also decreased when ambient CO2 was increased but remained 136% greater than the thermoneutral control level. All other parameters remained near their heat stress (40 °C) level during the elevation of ambient CO2. These data indicate that heat-stress-induced depression of miduterine arterial flow is vasoactively regulated, and cause-effect related to both arterial pH and PCO2, and thermoregulatory Shunting of blood to heat-dissipating surfaces.