Effect of day length and reproductive state on diel rhythms of luteinizing hormone levels in the plasma of white‐crowned sparrows, Zonotrichia leucophrys gambelii

Abstract

AbstractPlasma levels of LH were measured through the course of 24 hours in photosensitive and photorefractory, adult male white‐crowned sparrows, Zonotrichia leucophrys gambelii, exposed to both long (20L, 4D) and short (8L, 16D) days. In photorefractory birds held on both long and short days there is an increase in plasma levels of LH late in the subjective day or soon after the onset of the scotophase. These levels remain high for most of the night and decline to low levels just after the onset of the photophase. In addition there is a second increase in circulating LH, 3–5 hours after the onset of the photophase, with a second minimum about 10 hours later.A similar rhythm occurs in photosensitive birds held on short days. Plasma levels of LH increase late in the day and remain high throughout most of the night. Lowest levels were measured just after onset of photophase. In contrast, circulating LH in photosensitive birds exposed to long days showed no discernable diel rhythm. During the night, plasma levels of LH of photorefractory birds, and also photosensitive birds on short days, are as high as those of photosensitive birds on long days.