Changes and Interrelationships among Luteal LH Receptors, Adenylate Cyclase Activity and Phosphodiesterase Activity during the Bovine Estrous Cycle

Abstract

Changes and interrelationships among the cellular mechanisms that may regulate luteal progesterone synthesis during the bovine estrous cycle were studied. Corpora lutea (CL) were enucleated from 30 cows via a transvaginal incision on d 4, 7, 10, 13, 16 and 19 following estrus (estrus = d 0). Mean corpus luteum weight, and luteal progesterone and plasma progesterone concentrations increased (P less than .05) from d 4 to 7 or 10, and declined following luteal regression (d 19). Unoccupied LH receptor (UOR) concentrations increased (P less than .05) more than fourfold from d 4 (38 fmol/mg protein) to d 16 (173 fmol/mg protein) before declining (P less than .05) by d 19 (30 fmol/mg protein). The dissociation constant for UOR concentrations increased (P less than .05) during the estrous cycle. Concentrations of occupied LH receptors (OR) were less (P less than .05) on d 7 than other days; however, the total number of OR/CL increased fourfold from d 4 (47 fmol/CL) to d 10 (221 fmol/CL) and remained similar thereafter. Basal adenylate cyclase, LH-activated adenylate cyclase, and Gpp(NH)p-activated adenylate cyclase activities were greatest (P less than .05) on d 7 to 16 as compared with d 4 and 19. Luteinizing hormone stimulated (P less than .05) adenylate cyclase activity relative to basal activity on d 7, 10, 13, and 16; whereas, Gpp(NH)p stimulated (P less than .05) adenylate cyclase activity relative to basal activity at each period. Phosphodiesterase was 46% greater on d 19 as compared with d 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicle-Stimulating Hormone, Human Chorionic Gonadotropin, and Prolactin Receptors in Hamster Corpora Lutea or Dispersed Luteal Cells during Pregnancy1

“…For example, in the ewe, less than 0.5% of the total number of luteal LH binding sites are occupied by endogenous LH [18]. Occupied LH receptor concentrations compose about 2% of total receptor number in the bovine CL during the estrous cycle [19]. Rats hypophysectomized on the day of ovulation show by Day 5 a rapid decline in luteal hCG binding sites, both occupied and unoccupied, to 14% and 36%, respectively, compared to intact Day 5 pseudopregnant animals [20].…”

Evaluation of in Vitro Culture Conditions to Demonstrate Pregnancy-Dependent Changes in Luteal Function in the Pig1

“…FAX: (403) 492-9130. the number and size distribution of luteal cells in the CL of pigs [16] and sheep [17]. Correlations among LH/hCG receptor number and affinity and changes in luteal or serum progesterone concentrations have been found in the cow [18], sheep [19], and horse [20]. However, such relationships have not been established for the pig.…”

Progesterone Stimulation by LH Involves the Phospholipase-C Pathway in Bovine Luteal Cells

“…It has been proposed that phosphorylation by PKA stimulates cholesterol transport and P4 production, whereas phosphorylation by PKC may inhibit this process [1,2,4,5,[15][16][17]. However, a number of studies have suggested that P4 prod uction is directly stimulated by both intracellular pathways (PLC-PKC and cAMP-PKA) [6][7][8][9][10][11][17][18][19].…”

“…The mechanism of LH action induces stimulation of multiple signal transduction pathways in luteal cells [3]. Cyclic AMP (cAMP), which is induced by adenylate cyclase activation, is considered to be a primary second messenger of the LH action [4][5][6]. In bovine luteal cells, LH has been s h o w n t o s t i m u l a t e i n o s i t o l p h o s p h a t e accumulation and intracellular Ca 2+ , suggesting that LH activates not only adenylate cyclase but also inositol phospholipid-specific phospholipase-C (PLC) [7][8][9][10][11].…”