Influences of secretory activities in rat submandibular glands on tissue kallikrein circulating in the blood

Abstract

SUMMARYChanges in serum levels of rat tissue kalljkrein (rKl) in venous blood were measured, using a newly developed radioimmunoassay, before and after autonomic nerve stimulations of submandibular salivary secretion. rK1 secreted into saliva under these conditions was measured by radioimmunoassay and by enzymic activity assay, using the fluorogenic peptide substrate D-Val-Leu-Arg-7-amino-4-trifluoromethylcoumarin (AFC). Following an overnight fast, serum rK I concentration was 30-40 ng ml-'. Unilateral electrical stimulation of the submandibular sympathetic nerve supply (at 50 Hz in bursts of 1 s every 10 s for 60 min) evoked a small flow of saliva with a very high rK I concentration, resulting in a large output of rK l of 2104.4 + 603 5 jug (n = 6). Such stimulation caused a large degranulation of granular duct cells and a corresponding reduction in glandular rK 1 content. Unilateral electrical stimulation of the parasympathetic nerve supply (at 5 Hz continuously for 60 min) evoked a copious flow of saliva with a very low rK1 concentration, resulting in a low output of rK 1 (18 1 + 4.9 jug; n = 6). Despite these large differences in salivary outputs of rK1, serum concentrations of rK1 were increased similarly following either sympathetic or parasympathetic stimulation by 48 and 46 %, respectively. If the submandibular duct was briefly obstructed during sympathetic stimulation, inducing leakage and glandular oedema, then serum rK I increased greatly (40-fold); a similar increase to that seen by others in previous studies without deliberate obstruction. Four days after bilateral submandibular-sublingual sialadenectomy serum rK 1 concentration was reduced by approximately 50 %. The results indicate that submandibular glands normally contribute to circulating levels of rKl in rats, but this contribution is independent of the amounts of rKl secreted into saliva by sympathetically induced exocytosis, and is likely to arise from basal vesicular transport. However, if glandular leakage occurs during sympathetic stimulation of submandibular secretion this then causes increases in the circulating levels of rK1 that correlate with the large amounts being secreted into saliva.

The enzymic potential of tissue kallikrein (rK1) in rat submandibular saliva depends on whether it was secreted via constitutive or regulated pathways

“…The salivary flow rates, protein concentrations and activities and immunoreactive rK1 as measured by radioimmunoassay in the salivas obtained during the first series of experiments are summarized in Table 1. The mean enzymic activity of rKI in sympathetically evoked salivas was nearly 1000-fold greater than that in parasympathetically evoked, as found previously (Anderson et al 1995;Garrett et al 1995). Neither incubation at 37°C separately or mixed nor trypsinization of salivas resulted in any detectable changes in the rKI enzymic activities shown in Table 1.…”

Systemic and Portal Vein Delivery of Human Kallikrein Gene Reduces Blood Pressure in Hypertensive Rats

“…It has been reported that human tissue kallikrein level in normal human semm is about 3.5 ng/ml (Shimamoto et al, 1984) and the rat tissue kallikrein level in normal rat semm is 35^0 ng/ml (Garrett et al, 1995). The level ofhuman tissue kallikrein in the circulation of hypotensive ttansgenic mice expressing human tissue kallikrein is 50-300 ng/ml, which is at least 10-to 60-fold higher than those in normal human plasma.…”

“…Reduced urinary or renal kallikrein levels have also been observed in a number of genetically hypertensive rats (Ader et al, 1985;Favaro et al, 1975;MargoUus et al, 1972;Geller et al, 1975). The rat tissue kallikrein gene has been linked with hypertension by restriction fragment length polymorphisms and co-segregation studies in a hypertensive rat model (Woodley-Miller et al, 1989;Pravenec et al, 1991).…”

In Vivo Gene Transfer To Salivary Glands

“…Previously, Lal et al (1992) Isenman and Rothman, 1977;Garrett et al, 1995). We reasoned that if this were true, salivary glands might prove to be a valuable target site for systemic gene therapeutics.…”