Subcellular Localization of Hypothalamic Luteinizing Hormone

Abstract

Ultracentrifugation and sucrose gradient separation techniques have been applied to study of the subcellular distribution of hypothalamic luteinizing hormone (LH). Subcellular particle-bound LH accounted for 42% of the total LH while cytoplasm contained 58% of the total immunoassayable LH in these extracts. 70% of particle-bound LH was present in the P₂ fraction and most of the particle-associated LH was found in subfractions of P₂ rich in synaptosomes but poor in myelin and mitochondria. While actual amounts of LH in the P₃ and P₄, the microsomal fractions, were relatively small, the concentration of LH, expressed as nanograms per milligram of protein was quite high. Both content and concentration of LH in the nuclear pellet, P₁, were substantially lower. These findings provide further framework for speculation on the role of brain-based LH.

Hypothalamic Prolactin: Characterization by Radioimmunoassay and Bioassay and Response to Hypophysectomy and Restraint Stress

“…Each persists in the brain for at least 7 months after hypophysectomy indicating some independence from the anterior pituitary. Data have also been reported relating to the ontogeny [15], subcellular distribution [6,17], secretory control [5,7,9], and possible roles [2] for these brain-based proteins.More recently, a prolactin-like substance has been ident ified in the rodent brain, primarily utilizing immunohisto chemical identification [10,12,13,25,26]. The present study describes biochemical, immunologic, and biologic characterization of this protein from the rat hypothalamus.…”

Hypothalamic Luteinizing Hormone Increases Dramatically following Intracerebroventricular Injection of Colchicine

“…Several lines of evidence, including long-term (up to 7 months) persistence of LH in the brain following hypophysectomy at levels not significantly different from intact controls also suggests, but does not prove, that some brain LH is made in situ in the brain [7]. Further, study of the subcellular distribution of brain-based LH has shown that it is largely associated with subcellular fractions rich in synaptosomes but poor in myelin and mitochondria [10]. This observation, along with the demonstration that release of LH from hypothalamic slices can be stimulated by potassium-induced depolariza tion [9], supports the idea that brain LH may act as a neuro transmitter or neuromodulator, transsynaptically, in roles hitherto unsuspected and totally separate from its classical assignment as a reproductive hormone of pituitary origin.…”

“…Parlow. Details of the methodology used in this laboratory have been previously reported [8][9][10], Rat LH-RP-2 was used to develop the assay standard curves. Protein concentrations were de termined by the method of Waddell \ 19].…”

Feedback of Follicle-Stimulating Hormone to Inhibit Luteinizing Hormone and Stimulate Follicle-Stimulating Hormone Release in Ovariectomized Rats

“…Alterna tively, there may be FSH-secreting neurons within the hypothal amus which release FSH and inhibit the release of LHRH either directly, or indirectly via intemeurons. Indeed, there is evidence to suggest the existence of LH-containing neurons within the hypothalamus [21,22], Plasma FSH was statistically unchanged after intraventricu lar injection of saline or 0.5 pg of o-FSH. Following the next higher dose (4 pg), there was a significant, progressive elevation of plasma FSH above the level of the controls throughout the 12 h of experiment.…”