Hypothalamus
Arcuate Nucleus
Dopamine (DOPA)
TRH, Vasopressin, Oxytocin
Blood Vessel
Pituitary Gland
ANTERIOR PITUITARY
Lactotropes
Prolactin (PRL)
Testes & Ovaries
POSTERIOR PITUITARY
Oxytocin
During suckling, a neural signal afferent from the nipple relays sensory information through the spinal cord to the paraventricular and arcuate nuclei in the hypothalamus, which downregulates DOPA secretion and upregulates TRH secretion
Dopamine (DOPA)
TRH, Vasopressin, Oxytocin
PRL alters activity of Nitric Oxide Synthase which induces vasoconstriction in the periphery
Lactotropes
DOPA acts on D2 receptors in lactotropes causing hyperpolarizationdecrease activity of adenylyl cyclaseintracellular [Ca2+] decreasesintracellular [K+] increasesTRH acts on Gq protein-coupled TRH receptor in lactotropes
Prolactin (PRL)
Testes & Ovaries
PRL is a weak gonadotropin, and can stimulate the ovaries in females and testes in males
Oxytocin
Oxytocin triggers smooth muscle contraction in mammary gland and is necessary for milk letdown
PRL acts on PRL-Receptor, a Type I Cytokine receptor encoded by the PRLR gene, which activates JAK/STAT kinases