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The pathophysiology of cystic fibrosis (CF), the secretory properties of CF cells and conductance studies of CF cells and membranes suggest that the basic defect of CF is an abnormality of regulation affecting a broad spectrum of functions. Prolactin (PRL) was proposed as the putative regulatory factor, because the multifarious activities of PRL, especially the well documented osmo- and electrolyte regulatory effects, can be related to all of the symptoms of CF. These include salt loss in sweat, abnormal mucus production, impaired intestinal digestion and absorption, male infertility, delayed puberty, failure to thrive, etc. Additionally those tissues in lower vertebrates in which PRL activity has been demonstrated are phylogenetically related to many of the tissues affected in CF.

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1. The elevated (Cl) of sweat from cystic fibrosis (CF) skin reverted to normal after the skin had been grafted onto immunoincompetent, congenitally athymic mice [N'NIH(S)-NU]. 2. The sweat (Cl) of CF skin grafts unlike that from normal skin did not increase when the host mice were injected with antibodies to human prolactin (hPRL). 3. One explanation for the above observations postulated a structurally modified PRL in CF patients. Circulating PRL in CF appears to contain a larger amount of glycosylated variants than that of healthy individuals.

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Because prolactin has been implicated in the transport of electrolytes in several mammalian tissues, we have looked for the presence of prolactin in human eccrine sweat glands where a primary isotonic secretion, rich in sodium chloride, is produced and subsequently modified by recovery of some sodium and chloride in excess of water. Sweat glands were microdissected from skin biopsies and then fixed overnight in phosphate-buffered 4% formaldehyde. The fixed tissue was dehydrated (to 95%) in ethanol and then embedded in glycol methacrylate. Sections were cut (5 microns) and immunostained with antihuman prolactin (NIDDK IC2) and the specifically-bound antibody was visualized using a biotinylated second antibody and Vector ABC reagents. Prolactinlike immunoreactivity was localized in the clear cells of the secretory coil and, to a much lesser extent, in the basal layer of duct cells. In many of the clear cells, the immunoreactive material appeared as a lateral strip and occasionally, in favorable sections, as a horseshoe of reaction product a few microns in from the apical and lateral membranes. In a subset of clear cells, with more euchromatic nuclei and a long, thin cellular profile, the immunostaining was more intense and was localized in a more juxtanuclear position. Controls for endogenous peroxidase, and those using normal serum or antihuman prolactin serum preabsorbed with purified human prolactin, gave no peroxidase localization in the tissue. These results are important because 1) they represent the first demonstration of prolactin or a prolactinlike substance in the sweat gland, 2) the prolactinlike material was localized to clear cells that are thought to be responsible for much of the fluid secretion, 3) the necessity for prolactin or pituitary extract in primary cultures of sweat gland epithelium is potentially explained, although not fully understood, and 4) it means that further studies concerned with the possible influence of prolactin on ion transport in the sweat gland are warranted.

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Cystic fibrosis (CF) is a lethal, genetically transmitted disease of Caucasian populations. Its prevalence is highest (ca 1:2000 live births) among Western and Central Europeans and their descendants. Major clinical symptoms are chronic, obstructive, pulmonary disease, impaired intestinal digestion and absorption and elevated concentration of salt in sweat. The last is important, not only for diagnosis, but because it is an example of an electrolyte transport defect present in other epithelial tissues. Numerous other clinical manifestations are generally present. The history of prolactin (PRL), especially its role in osmoregulation, is outlined and related to the symptomatology and electrolyte defect of CF. Data are presented showing the relation of PRL to regulation of sweat electrolytes and its presence and probable synthesis in the coil of the human sweat gland. The basic biochemical defect of CF has not yet been elucidated, but recent research has shown that it is probably an abnormality of a regulatory factor. We propose that PRL is a likely candidate. The large variety of functions of PRL, in particular the regulation of the transport of sodium and chloride across epithelial membranes, and the regulation of mucus production, can be matched to the major disease symptomatology. Additionally, every other one of the multiple abnormalities of CF can be associated with described activities of PRL. In lower vertebrates epithelial tissues regulated by PRL are phylogenetic progenitors of affected tissues in CF. In the human, these tissues contain cells of the Diffuse Neuroendocrine System, or APUD cells, that show PRL-like immunoreactivity, or overt synthesis of the hormone. Thus, the regulatory activity of these tissues could be paracrine. The geographic distribution and the dietary habits of early Caucasians are examined. It appears that the Neolithic revolution, with the necessity of adapting to agriculturally produced foods, i.e. milk and wheat, could have brought about the genetic selection of post-translational variants of PRL. It is suggested that the combination of two or more of these mutations in the same individual may be responsible for CF. This is illustrated with proposed models of CF inheritance. We conclude by postulating that PRL acts at the level of the target cell by triggering (in conjunction with a steroid) the gene expression of unique proteins; these act as intermediaries of PRL activity; two or more abnormalities of these proteins when present in an individual produce CF; the protein abnormalities are the consequence of nutritional and ecological pressure.

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Using a double-antibody immunoperoxidase technique, we demonstrated human prolactin-like material in some cells of the secretory coil and in luminal duct cells of sweat glands of human skin which had been carried as grafts on mice for 32-35 weeks. It therefore seems likely that a population of cells in the secretory coil synthesizes prolactin and can be considered as diffuse peripheral endocrine cells. The prolactin may function locally to regulate sweat electrolyte concentration.

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The purpose of this study was to elucidate the possible relationship between defective PRL and elevated sweat Cl in CF patients. Full thickness human skin was grafted onto the back of immunoincompetent, nude congenitally athymic mice. This study indicated: 1) that when skin from CF patients with high sweat chloride concentrations was grafted, the chloride concentration of sweat from the grafts was the same as of sweat from grafts of normal skin; and 2) that administration of anti-hPRL to the mice bearing the CF grafts did not increase the chloride concentration of the sweat as it had in normal skin grafts. 3) that CF may involve defective PRL production leading to failure of regulation of Cl channels in affected epithelia, 4) that the athymic mouse is a useful model for studying PRL activity in the pathophysiology of sweating of CF patients.

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The purpose of this study was to determine whether the availability of PRL modulates the chloride concentration of human sweat. Full thickness human skin grafted into the back of immunoincompetent, nude, congenitally athymic mice heals in about 6 to 10 weeks and survives the life of the mice. Mice have no sweat glands in the back so this system provides a useful model for study of the physiology and pathology of human sweat glands. The graft can be induced to sweat and the sweat collected for analytical studies. Presumably normal skin obtained from 7 individuals undergoing reconstructive surgery was grafted successfully into 11 mice. On 49 occasions sweat was induced by pilocarpine iontophoresis and collected for 45 min. The chloride concentration was 12.9 +/- 6.7 meq/liter, values typical of normal human sweat. Nine mice bearing grafts were injected with rabbit anti-human PRL (hPRL). The chloride concentration of sweat obtained a day later was significantly elevated. The concentration generally increased after a second and sometimes a third injection of anti-PRL. The average maximum sweat chloride obtained was 61.9 +/- 8.25 meq/liter. Serum of rabbits that had not been exposed to hPRL was prepared and diluted in the same way as the anti-hPRL. The chloride concentration of sweat of 3 mice that received the preparation for several days remained unchanged at the low normal level. We conclude that depletion of PRL increases the concentration of chloride in human sweat.

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