Human Reproduction, Vol. 16, No. 12, 2508-2514,
December 2001
© 2001 European Society of Human Reproduction and Embryology
Follicular fluid responds endothermically to aqueous dilution
1 University of Nottingham, Division of Animal Physiology, School of Biosciences, Sutton Bonington Campus, Loughborough LE12 5RD, 2 University of Edinburgh, Department of Veterinary Clinical Studies, Easter Bush, Midlothian and 3 University of Glasgow, Department of Chemistry, Glasgow G12 8QQ, UK
BACKGROUND: Studies suggest that ovarian follicles are cooler than their surrounding tissues. The mechanism of this remarkable phenomenon is unclear. We postulate that endothermic reactions accompany the growth-associated hydration of follicular fluid. METHODS: We performed two types of experiment, using human and animal follicular fluids. In the first, saline (50 µl) was injected into follicular fluid (500 µl) held in an equilibrated incubator, with monitoring of sample temperature. In the second, an adiabatic microcalorimeter recorded thermal shifts after injection of buffer (10 µl) into previously dialysed samples (1.4 ml). The relevance of changes observed was assessed by mathematical modelling. RESULTS: In the incubator study, 9/17 bovine and 6/12 human fluids showed a temperature fall (0.05–0.2°C). Cooling was delayed by up to 2 min but sustained for 7–25 min. Remaining fluids showed no change. In the microcalorimeter, 4/9 human, 4/6 bovine, 5/5 porcine and 1/4 equine samples showed an endothermic response. Remaining samples showed either no response (bovine) or exothermy (human, equine). Pre-concentration of human follicular fluid amplified the endothermy or reversed the exothermy. Modelling indicated that the incubator-type response was of appropriate magnitude to explain follicular hypothermy. CONCLUSION: Follicular fluid responds endothermically to aqueous dilution and may contribute to follicular cooling during growth.
Key words: endothermy/follicle/hydration/microcalorimetry/temperature
4 To whom correspondence should be addressed. E-mail: martin.luck{at}nottingham.ac.uk
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