Time domains of the hypoxic ventilatory response in ectothermic vertebrates

Over a decade has passed since Powell et al. (Respir Physiol 112:123–134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123–134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O2 supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more ‘holistic’ fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind

Effects of growth hormone replacement on cortisol metabolism in hypopituitary patients treated with cortisone acetate

Growth hormone (GH) replacement may inhibit 11 beta -hydroxysteroid dehydrogenase type 1 (11 beta HSD1) activity, resulting in diminished conversion of cortisone to cortisol. Moreover, GH replacement may lower bioavailability of hydrocortisone tablets. Therefore, substitution therapy with cortisone acetate could be disadvantageous during GH replacement. We conducted a randomized, placebo-controlled GH replacement( 1 to 2 U GH/day) study during 6 months, followed by a 6-month open extension study (2U GH/day). Twelve men and 12 women with GH deficiency, of whom 17 received cortisone acetate (25 to 37.5mg/day), participated. Eight patients were randomized to placebo initially. At baseline, after 6 and 12 months, urinary cortisol and cortisone metabolites were measured. No changes in urinary cortisol metabolites were observed after 6 months placebo (n= 8). After 6 months GH the urinary (tetrahydrocortisol + allotetrahydrocortisol)/tetrahydrocortison ratio ((THF + alloTHF)/THE ratio) was unaltered in cortisone acetate treated patients (n = 17) and in patients with intact adrenal function (n = 7), whereas after 12 months GH the ( TH F + alloTHF)/THE ratio decreased only in cortisone acetate treated patients(l dropout, n=9). Urinary THF and alloTHF were higher in cortisone acetate treated patients than in patients with intact adrenal function before GH and remained so after 12 months GH (p <0.05 to p <0.01). The sum of cortisol + cortisone metabolites did not change after GH in either group. The urinary free cortisol/free cortisone ratio, presumably reflecting renal 11 beta HSD2, activity. tended to decrease in cortisone acetate treated patients (p <0.07 and p <0.05 after 6 and 12 months GH, rrspectively). as well as in patients with intact adrenal function (p <0.05 and a decrease in five/ six patients after 6 and 12 months GH, respectively). In conclusion. these results suggest that GH replacement decreases 11 beta HSD1 activity. which becomes manifest in patients receiving cortisone acetate substitution therapy. 11 beta HSD2 activity is unaltered or may even be increased. It is unlikely that the bioavailability of conventional doses of cortisone acetate is impaired after GH replacement

11 beta-hydroxysteroid dehydrogenase activity in proteinuric patients and the effect of angiotensin-II receptor blockade

Background It has been suggested that an altered setpoint of the 11betaHSD-mediated cortisol to cortisone interconversion towards cortisol contributes to sodium retention in nephrotic syndrome patients. We studied the parameters of 11betaHSD activity in proteinuric patients, in particular its activity at the kidney level. We also studied the effect of angiotensin-II receptor blockade on the parameters of 11betaHSD activity. Materials and methods Serum cortisol/cortisone ratio and the urinary ratios of (tetrahydrocortisol + allo-tetrahydrocortisol)/tetrahydrocortisone [(THF+allo-THF)/THE] and of urinary free cortisol/free cortisone (UFF/UFE) were measured in eight proteinuric patients and compared with eight matched, healthy subjects. Patients were subsequently studied after 4 weeks' treatment with losartan 50 mg day(-1) and placebo, respectively. Results No significant differences between the proteinuric patients and the healthy subjects were observed in the serum cortisol, serum cortisone, serum cortisol to cortisone ratio, or in the urinary excretions of THF, allo-THF, THE, sum of cortisol metabolites, or the (THF + allo-THF)/THE ratio. Urinary free cortisol excretion and the UFF/UFE ratio were lower in the proteinuric patients than in the healthy subjects (56+/-21 vs. 85+/-24 pmol min(-1), P Conclusions Increased renal inactivation of cortisol in proteinuric patients does not support the contention that altered 11betaHSD activity contributes to sodium retention in patients with nephrotic syndrome. Losartan 50 mg d.d. reduces mean arterial pressure and proteinuria, but does not exert a significant effect on the cortisol to cortisone interconversion