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Prolactin immunoreactivity has been detected in human tears and in lacrimal glands, and it has been suggested that this hormone might be a modulator of lacrimal secretion as well as a component of lacrimal gland fluid. The present study was designed to confirm the immunocytochemical localization of prolactin in the rat lacrimal gland, to determine the source of the prolactin, and to evaluate the acute effects of prolactin on lacrimal secretory function. We have confirmed that prolactin-like immunoreactivity is present in secretory vesicles of acinar cells of male and female Sprague-Dawley rats. Prolactin message was present at detectable levels in RNA extracts of lacrimal glands from males, indicating that at least a component of the prolactin-like immunoreactivity was the product of synthesis within the lacrimal glands. Crude membrane fractions from acini isolated from males bound 43.1 +/- 3.2 femtomoles prolactin/mg protein (mean +/- standard error of the mean; n = 6), which was significantly (P less than 0.01) more than comparable fractions from females (15.4 +/- 2.4 fmoles/mg protein, n = 6). Preincubating membranes at 65 degrees for 20 min to release endogenous ligands increased prolactin binding to 84.8 +/- 20.8 fmoles/mg protein for males and 63.8 +/- 17.4 fmoles/mg protein for females (P greater than 0.1), suggesting that, on average, similar numbers of receptors are expressed in acinar cells of male and female rats but a larger fraction of the receptors is occupied by endogenous prolactin-like peptides in females. Because prolactin binding triggers prolactin receptor internalization in various cell types, we propose that the prolactin-like immunoreactivity in lacrimal acinar cells of females has been accumulated from the circulation, while the immunoreactivity seen in males results, at least in part, from de novo synthesis. Ovine prolactin at concentrations of 10-20 ng/ml inhibited carbachol-induced peroxidase release by 19.6% +/- 6.9% (n = 8, P less than 0.02) but failed to alter peroxidase release in the absence of carbachol. These observations suggest that prolactin might function as an endocrine, paracrine, or autocrine modulator in the lacrimal gland.
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
April 1971,
The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
October 1992,
Acta ophthalmologica,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
January 1992,
Investigative ophthalmology & visual science,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
January 1984,
Scanning electron microscopy,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
September 1989,
Investigative ophthalmology & visual science,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
December 1978,
Cell and tissue research,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
January 1989,
Acta anatomica,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
April 1994,
Journal of the autonomic nervous system,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
January 1998,
Advances in experimental medicine and biology,
A K Mircheff, and
D W Warren, and
R L Wood, and
P J Tortoriello, and
R L Kaswan
July 1983,
The American journal of physiology,
