LACRIMAL SECRETION STIMULANTS - SIGMA-RECEPTORS AND DRUG IMPLICATIONS

H-3-DTG (1.3-di(2-(5-H-3]tolyl)guanidine) or H-3-haloperidol was added to sigma-receptors (25 nM) in the presence of 25 nM spiperone and inc ubated with increasing concentrations of bromhexine derivatives (pheny lalkylamines; 10(-9) to 10(-2) M) in membrane homogenate suspensions. IC50 values for two derivatives ranged from 3.2 to 8.8 nM for both rad ioligands. A preferred derivative, 7A (N, N'-dimethyl-2-phenyl-ethylam ine), yielded an IC50 of 7.8 nM for H-3-haloperidol but showed much le ss affinity in displacing H-3-DTG (IC50-900 nM). Applying the technic of Bromberg (Exp. Eye Res. , 40: 313-320, 1985], in vitro protein secr etion rates were measured following stimulation of either lacrimal gla nd slices or isolated, intact lacrimocytes with the compounds. In vitr o protein secretion rates exhibit a dose-response relationship with in creases in protein release up to a concentration of 10(-8) to 10(-4) M for various derivatives of bromhexine and 10(-4) M for carbachol. By means of Schirmer strips, tear fluid was collected over a five minute period at 10 and 60 minutes post-dosing following the topical applicat ion (50 mul) to the right eye of New Zealand white rabbits (n = 20-24) of 7A at various concentrations. Incubation of lacrimocytes with 7A a lone (10(-4) M), with haloperidol (10(-4) M) alone or in combination s how that 7A is acting as an agonist to stimulate protein release, wher eas haloperidol is acting as an antagonist to inhibit release. In vivo protein secretion rates also show a dose-response curve (at both 10 a nd 60 minutes post-dosing) for 7A that reach a statistically significa nt maximum in the dosed eye at a concentration of 0.15% w/v. Analysis of protein extracts using size exclusion HPLC shows an increase in sec retory proteins, particularly tear-specific prealbumin.