Face cooling-induced reduction of plasma prolactin response to exercise as part of an integrated response to thermal stress

Abstract

This study was designed to verify if the decrease in blood prolactin (PRL) induced by selective face cooling during exercise could be part of a response to specific body thermal stress. Five healthy trained male cyclists presenting a significant plasma PRL elevation to exercise were, on three occasions and at weekly interval, submitted to a submaximal exercise (approx. 65% VO2max) on ergocycle with and without selective face cooling. In absence of face cooling a first trial served to establish reference values for workload, heart rate and plasma PRL levels, the latter increasing markedly (450% of resting values) in these conditions. On a second trial but with workload maintained at reference values (222 +/- 9 W), a significant bradycardia was observed with face cooling; furthermore, plasma PRL response to exercise was significantly reduced (to 31% of original response). On a third trial with face cooling, workload had to be significantly augmented (242 +/- 10 W) to maintain heart rate at reference level (78% HRmax); in addition, plasma PRL response to exercise was almost unchanged compared to the reference-value level. The absence of a significant face cooling-induced decrease in sympathetic tonus, as evaluated through peripheral plasma catecholamines response, does not indicate a role for the autonomic nervous system in the face cooling-induced reduction of both heart rate and PRL responses during exercise. Assay of circulating peripheral beta-endorphins could indicate that the face cooling-induced PRL blunted response does not necessarily involve an opioid mediation.(ABSTRACT TRUNCATED AT 250 WORDS)

The prolactin responses to active and passive heating in man

“…These results suggest that thermoregulatory afferents, i.e. increases in core temperature, are probably the key stimulus for prolactin release, which is in agreement with previous work (Brisson et al 1989; Bridge et al 2003).…”

“…Hypothalamic dopaminergic neurones that secrete dopamine into the pituitary portal vessels also tonically inhibit the secretion of prolactin (Van de Kar et al 1996). Significant increases in prolactin (which peak at the point of exhaustion) are evident during exercise in the heat that leads to an intolerable thermoregulatory strain (Brisson et al 1989; Pitsiladis et al 2002). This suggests alterations in central serotonergic and dopaminergic activity, in response to the increased core temperature, that could contribute to the reduced motivation to continue exercise, and subsequently fatigue, in the heat.…”

Neck Cooling and Running Performance in the Heat

“…No data were provided regarding the effect of cooling the neck exclusively at rest compared with no cooling; however, data from this and another study (35) suggest that sustained cooling of the head or neck might offer a cumulative benefit to exercise undertaken in a hot environment. The effectiveness of any cooling intervention to alter physiological or neuroendocrinological variables seems to be dependent on the difference between the magnitude of the cooling and the thermal strain experienced (4,23), and the greatest benefits are often reported when the thermal strain is at its most severe (23). To date, no research has investigated the effect of sustained neck cooling on prolonged exercise performance.…”

“…On the basis of previous neck cooling literature (34,35), it was hypothesized that the additional performance improvement would occur as a result of a greater improvement in the perceived level of strain experienced and not as a result of the additional cooling affecting the physiological or hormonal response to the exercise. However, the effectiveness of cooling interventions has been shown to be dependent on the difference between the magnitude of the cooling and the thermal strain experienced (4,23) and so it is possible that sustained cooling may affect theses variables, and therefore, they were measured in the present study. The aims of the current study were to test this hypothesis and to investigate the effect of maintaining the neck at a reduced temperature, via the replacement of the CC, throughout the 90-min protocol.…”

Endocrine Function

“…During exercise in normobaric hypoxia, plasma prolactin was found increased [ 97 ], unchanged [ 93 ] or decreased [ 96 ], when compared to normoxia. A blunted prolactin response was observed during exercise in normoxia with concomitant face-cooling, suggesting that cold exposure may diminish the exercise-induced prolactine release [ 95 ]. After 7 weeks at high altitude, a prolactin increase coupled with testosterone decrease and progesterone increase, without any change in estradiol, probably due to chronic stressful conditions [ 18 ].…”