Oxytocin In Corpus Luteum Research Articles

Immunocytochemical localization of oxytocin in corpora lutea and luteinized cysts from anoestrous ewes stimulated with gonadotrophin-releasing hormone

Anoestrous Romney Marsh ewes with or without progesterone pretreatment were injected with multiple low-doses of gonadotrophin-releasing hormone followed by a single, larger bolus. Blood samples were taken at twelve-hourly intervals for progesterone radioimmunoassay. Ewes were slaughtered on day 3 or 5 after the bolus injection, and the ovaries were collected for histology and immunocytochemical examination for oxytocin-immunoreactivity. The corpora lutea of all ewes killed on day 3 had similar weights and morphology. The ovaries of those ewes which were not pretreated with progesterone also contained some luteinized cysts. Ewes slaughtered on day 5 were separated into 2 groups according to plasma progesterone profiles, which were either rising ('normal'), or falling after a transitory rise ('abnormal'). Those ewes pretreated with progesterone all had a 'normal' progesterone profile whereas, of 14 ewes not pretreated with progesterone, 6 were 'normal' and 8 'abnormal'. Corpora lutea were significantly lighter in the 'abnormal' group and the ovaries of most of these ewes also contained luteinized cysts. All corpora lutea and luteinized cysts showed staining for oxytocin-immunoreactivity although the staining intensity was variable. In corpora lutea from 'normal' ewes oxytocin was restricted to large luteal cells. In addition tissues from 'abnormal' ewes also contained many cells with an atypical elongated shape which stained for oxytocin-immunoreactivity. These results show that progesterone pretreatment is needed for both normal morphological and endocrine development of corpora lutea in anoestrous ewes stimulated with gonadotrophin-releasing hormone.

Concentrations of oxytocin-neurophysin prohormone mRNA in corpora lutea of sheep during the oestrous cycle and in early pregnancy.

Concentrations of oxytocin in corpora lutea from pregnant and non-pregnant sheep rose during luteinization to peak between days 5 and 9 after oestrus before falling to low levels on days 12 and 14. Concentrations of the 608-base mRNA encoding the oxytocin-neurophysin prohormone, measured by Northern blotting using a cRNA probe, were highest before day 5, and fell to low levels by day 9. The decline in oxytocin during the second half of the oestrus cycle and in pregnancy could therefore be accounted for by reduced luteal concentrations of oxytocin-neurophysin mRNA. The rate of decline in prohormone mRNA concentration between days 3 and 16 followed first order kinetics, suggesting that gene expression ceased early in the cycle. The lag between peak oxytocin-neurophysin mRNA and peak oxytocin concentrations may represent the time taken for post-translational processing of the prohormone.

Human ovarian oxytocin: Its source and relationship to steroid hormones

To determine the site of oxytocin in human ovaries and its relationship with ovarian steroids, oxytocin and steroid hormones were measured in ovarian tissues, ovarian vein, and peripheral blood. Corpus luteum had significantly higher oxytocin, estrone, estradiol, and progesterone concentrations than corpus albicans and ovarian stroma (p = <0.01 to < 0.001). Oxytocin concentrations in corpus luteum correlated significantly with estrone, estradiol, and progesterone. Oxytocin in corpus luteum increased from 14.0 ± 1.8 ng/gm of wet weight in early to 30.8 ± 0.9 ng/gm in midluteal phases (p = <0.001). Reverse phase high pressure liquid chromatography showed similarity between oxytocin in corpus luteum and synthetic oxytocin. Ovarian vein draining corpus luteum had significantly higher plasma oxytocin (11.8 ± 1.5 pg/ml) than those without corpus luteum (2.1 ± 0.2 pg/ml) or in the peripheral blood (2.9 ± 0.3 pg/ml) (p = <0.001). Oxytocin in corpus luteum correlated significantly with its ipsilateral ovarian vein level of oxytocin, estrone, progesterone, and 17α-hydroxyprogesterone. Our findings demonstrate that oxytocin is present and probably produced in corpus luteum and secreted into its ovarian vein; it may regulate corpus luteum release of progesterone, 17α-hydroxyprogesterone, and estrone.

Regression of the corpora lutea in sheep in response to cloprostenol is not affected by loss of luteal oxytocin after hysterectomy.

Concentrations of oxytocin in corpora lutea were reduced from 1706 to less than 15 ng/g wet wt after hysterectomy in sheep during the oestrous cycle. Hysterectomy also blocked the appearance of raised levels of oxytocin in ovarian and jugular venous plasma caused by cloprostenol. Administration of cloprostenol to hysterectomized ewes resulted in luteal regression, which occurred as rapidly as in intact animals. Therefore oxytocin in the corpus luteum during the oestrous cycle is unlikely to be involved in intraluteal events mediating prostaglandin-induced luteolysis.