Intraluminal volume homeostasis

Abstract

Volume homeostasis is a common physiological phenomenon for fluid secreting organs, such as exocrine and endocrine glands. It is a manifestation of a finite intraluminal space and an ever changing demand for secretory fluids. Volume homeostasis addresses issues of fluid secretion, storage and clearance for efficient functioning. Here we discuss the evidence gathered over the past 2-3 decades on serotonin’s role as a feedback inhibitor of secretion in the mammary gland, salivary gland, liver, pancreas, lung, thyroid gland and prostate gland. We propose that serotonin action is a common mechanism of regulating intraductal volume homeostasis. 

Figures and Tables

Figure 1 Mammary epithelial serotonin system and its mechanism of action. Diagramatic representation of mammary epithelial serotonin system. Mammary epithelial cells synthesize serotonin and secrete it into their surroundings. This serotonin acts in an autocrine-paracrine manner through its receptors. Among these, 5-HT₇ receptor has been localized to the baso-lateral side of the mammary epithelial cells. 5-HT through the 5-HT₇ receptor generates two signals; a cAMP-PKA signal and a cAMP-p38^MAPK signal. Serotonin reuptake transporter (SERT) is present on the apical membrane of the mammary epithelial cells and is involved in recycling and metabolism of mammary serotonin.

Table 1 Serotonin receptor expression in ductal organs