Photoperiod duration and energy balance in the pigeon.

Energy balance, and daily rhythms in feeding activity, body temperature (Tb), metabolic rate (O2 consumption), and RQ (CO2/O2) that affect that balance, were studied in pigeons when the duration of the photophase gradually lengthened (LP group) or shortened (SP group) from an initial starting point at LD 12:12. The end point of change for the LP group was LD 21:3, and for the SP group was LD 3:21. Standard laboratory conditions were in effect (moderate ambient temperature; ad lib food and water).

Daily cycles in body temperature, metabolic rate, and substrate utilization in pigeons: influence of amount and timing of food consumption.

Pigeons lived in individual chambers where instantaneous metabolic rate (MR; indirect calorimetry), body temperature (Tb), and substrate utilization (RQ) were measured 24 times each hour throughout the 12h:12h light:dark cycle. The amount of food consumed influenced the amplitude of the MR and Tb cycles, primarily by affecting the dark-phase segment of the cycle: when food was consumed ad lib, low-amplitude daily cycles in MR and Tb occurred in which levels in the dark phase were lower than in the light; during reduced food intake in restricted feeding or in fasting, high-amplitude cycles occurred primarily because nocturnal hypometabolism and hypothermia developed; in restricted feeding, the level of MR and Tb during the dark-phase segment of the cycle was directly related to short-term variation in amount consumed. The timing of food consumption primarily affected the light-phase segment of the MR and Tb cycles: when feeding was restricted to a time late in the light phase, these measures became depressed early in the light phase, and then greatly elevated near the scheduled time of feeding.

Infusion of dopamine at low concentrations stimulates the release of prolactin from alpha-methyl-p-tyrosine-treated rats.

Prolactin (PRL) secretion from the anterior pituitary gland is inhibited by dopamine (DA) released into the hypophysial portal vasculature from neurons in the hypothalamus. We have shown previously that DA also stimulates PRL secretion in vitro. Here we report that DA has a dual effect on PRL release in vivo.