Defective beta adrenergic response of cystic fibrosis sweat glands in vivo and in vitro

Abstract

Abnormal ductal NaCl absorption has been known as the only defect in cystic fibrosis (CF) sweat glands. We have fortuitously found that the secretory portion of CF sweat glands is also abnormal in that it failed to show a sweating response to beta adrenergic stimulation (isoproterenol, [ISO]) both in vivo and in vitro. For the in vitro sweat test, eccrine sweat glands were isolated from skin biopsy specimens of the forearm, cannulated, and stimulated to secrete sweat. All 14 isolated CF sweat glands failed to respond to ISO + theophylline (TH, as aminophylline), but 17 of 18 control glands responded with a mean rate (SR) of 1.1 nl/min per gland. Cholinergic responsiveness of isolated CF sweat glands was comparable with that of control glands. The in vivo sweat test was performed by intradermal injection in the forearm of 0.2 ml of 2.4 or 8 x 10-5 M ISO with or without 10-2 M TH (and 1.4 x 10-4 M atropine as a necessary anticholinergic agent). The beads of sweat secreted into the oil-filled sweat collection ring glued to the skin were then collected with a glass capillary under a stereomicroscope. Of 28 CF patients, 26 failed to show a secretory response to intradermal injection of ISO + TH, and 2 CF patients gave SR of <0.007 nl/min per gland in the first test but no response in the repeat test performed later. In contrast, all 35 age- and sex-matched control subjects responded with the mean SR of 0.72 nl/min per gland. Response of CF patients to epinephrine and phenylephrine was comparable with control, indicating that the alpha adrenergic responsiveness of CF sweat glands is not defective. A preliminary attempt was made to determine tissue cyclic AMP accumulation by radioimmunoassay in isolated sweat glands. No significant difference was observed between CF and control glands in their maximal accumulation of tissue cAMP in response to ISO or ISO + TH, except that the rise time of ISO + TH-induced cAMP accumulation in CF glands was significantly slower during the first 5 min of incubation. The data suggest that beta adrenergic regulation is abnormal in CF sweat glands and justifies further investigations into the mechanism of beta adrenergic regulation of the eccrine sweat gland in both normal and CF subjects.