Hypothalamic-Pituitary Vasculature: Evidence for Retrograde Blood Flow in the Pituitary Stalk1

Abstract

Retrograde transport of pituitary hormones in the pituitary stalk vasculature was investigated in anesthetized male rats in which the pituitary gland was intact and in animals in which the anterior pituitary, posterior pituitary, or entire pituitary gland had been removed 30 to 60 min before use. Blood was collected for 1.5 to 2 h by free flow from a single long portal vessel through a microcannula, the tip of which was pointed toward the hypothalamus. An arterial blood sample was obtained at the end of each collection of portal blood. The concentrations (ng\ml) of LH, TSH, prolactin, ACTH, α-MSH, and vasopressin, determined by radioimmunoassay, in portal plasma from rats with intact pituitary glands were as follows: LH, 2,320 ± 874 (mean and SE); TSH, 10,180 ± 1,471; prolactin, 4,858 ± 884; ACTH, 82 ± 17.0; a-MSH, 103 ± 17.8; vasopressin, 2.4 ± 1.0. The concentrations of these hormones in arterial plasma of these rats were as follows: LH, <20; TSH, 149 ± 22; prolactin, 25 ± 5.0; ACTH, 0.36 ± 0.05; α-MSH,...