Effect of prolactin inhibition under heat exposure on water intake and excretion of urine, sodium and potassium in bulls

Abstract

Abstract. Six Holstein bulls were housed in a climate-chamber under constant light regimen and after two weeks of preconditioning at 15°C, 60% relative humidity RH (day) and 12°C, 60% RH (night) were subjected to two weeks of heat exposure. This involved one week at 30°C and 60% RH (day) and 25°C and 60% RH (night) and a further week at 35°C, 60% RH (day) and 30°C, 60% RH (night). Three bulls were untreated (group I) and 3 bulls were treated (group II) just before and during heat exposure with a prolactin inhibitor to study the possible physiological role of prolactin on the regulation of water, potassium and sodium. Serum prolactin levels increased significantly (P < 0.01) in group I from the control value of 6 ng/ml to 33 and 44 ng/ml when the ambient temperature was increased (weeks 3 and 4) and then decreased to 21 and 12 ng/ml after reduction in temperature during weeks 5 and 6, respectively. For group II prolactin values decreased under the treatment with the prolactin inhibitor to 0.5 ng/ml and remained at this level throughout the experiment. GH levels were unaffected by heat treatment or by treatment with prolactin inhibitor. There were no differences between groups I and II in respiratory rate, pulse rate and rectal temperature. Water intake increased in both groups under heat exposure but decreased significantly afterwards only in group II. Differences in urinary excretion volume and blood serum osmolality were not significant. Urinary potassium and sodium excretion were unchanged in group II but increased with heat exposure in group I. During heat exposure 2 bulls of group II lost weight despite maintaining food intake.

Exercise-Induced Blood Prolactin Variations in Trained Adult Males: A Thermic Stress More than an Osmotic Stress

“…The existence of a relation between body temperature and PRL is not a newly ob served phenomenon: it has been demon strated in humans [Dumoulin et al, 1980;Lahiri et al, 1981;Mills and Robertshaw, 1981;Ruppert et al, 1982], in rats [Mueller et al, 1974;Tacheei al., 1978;Rosenberg el al., 1980] and cattle [Hill et al, 1980: Schams et al, 1980. Our observations ( fig.…”

“…Also, these blood PRL increases in the exercising subjects receiving a water intake sufficient to maintain a euhydrated state (as appreciated by blood osmotic pressure mea surements) does not explicitely support in humans the idea postulated by Schams et al [1980] of a role for PRL, at least in bulls, in eliciting necessary thirst responses during heat exposure. That blood volume changes could favor an increase in blood PRL levels was not considered since increase in blood volume by hypertonic and hypotonic intra venous infusions did provoke divergent blood PRL variations in humans [Buckman and Peake, 1973].…”

L‐DOPA attenuates prolactin secretion in response to isolation stress in Holstein steers

“…; Schams et al . ) and a suppression of dopaminergic neurons is observed when PRL increase occurs due to high temperature (Tucker et al . ).…”

Prolactin and Osmoregulation in Vertebrates

“…Chronic hyperprolactinemia in rats promoted water intake and a consequent increased blood volume and decreased plasma osmolality; incremental water intake was inhibited by CB154-induced reduction in hyperprolactine mia [101]. In the bull, there appears to be both prolactin-de pendent and prolactin-independent drinking regulation [178]. The dipsogenic action is most likely on the central nervous system rather than on epithelial surfaces, but such an action would regulate the exposure of the latter to fluids…”