Current methods for obtaining venous blood from the reproductive organs of livestock often have a low rate of success or involve intensive surgical procedures that may impair ovarian function. Therefore, the caudal vena cava was catheterized via the lateral saphenous vein to determine the feasibility of using this method for chronic sampling of blood draining from the reproductive organs of ewes (n = 6), cows (n = 6), and gilts (n = 7). Blood samples were collected at 2-cm (ewes and gilts) or 5-cm (cows) intervals during insertion of catheters. Correct placement, defined as the position at which plasma concentrations of progesterone or estrogen were at least threefold greater than in jugular venous plasma, varied among species and among animals within species. It seemed, however, that a majority of catheters would be placed correctly if secured at 48 to 52 cm in ewes, 52 cm in gilts, and 90 to 100 cm in cows. Saphenous vein catheters were secured for sequential sampling of vena caval blood during the follicular phase of ewes (n = 25), cows (n = 4), and gilts (n = 5). Catheters remained patent for the duration of sampling in all individuals. Concentrations of estrogen in jugular and vena caval plasma were correlated (ewe P less than .0003; cow P less than .0001; gilt P less than .0001). Profiles of progesterone and estrogen revealed an episodic pattern of secretion in vena caval but not jugular plasma. Catheterization of the vena cava via the saphenous vein is a relatively simple and noninvasive method for obtaining blood containing uterine and ovarian hormones before their metabolism.

To investigate the coordinate developmental expression of low-density lipoprotein (LDL) receptor, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, sterol carrier protein 2 (SCP2), steroidogenic acute regulatory protein (StAR), and cytochrome P450 side-chain cleavage (P450scc) enzyme messages throughout the pig estrous cycle, RNase protection analysis was performed using homologous (partially cloned) porcine sequences. Total RNA was isolated from ovarian tissues from unstimulated prepubertal gilts and gilts stimulated with eCG (Day -3) and hCG (Day 0) to induce follicular growth and ovulation. Specific transcripts (relative to 18S rRNA) were quantified in immature ovaries, preovulatory follicles (> or = 5 mm), corpora lutea (CL), and corpora albicantia. As an index of steroidogenesis, tissue progesterone content (per microgram protein) was low in the unstimulated ovary and preovulatory follicles, and it began to increase 4 days post-hCG, peaked at 12 days, and returned to preovulatory concentrations by 20 days post-hCG. HMG-CoA reductase mRNA was expressed at low levels and did not change significantly throughout the estrous cycle. The amount of LDL receptor mRNA increased approximately 6-fold after eCG stimulation and was expressed at similar concentrations in both preovulatory follicles and functional CL. Expression of SCP2 mRNA did not differ among the four tissue types but tended to be highest in midcycle (Day 12) CL compared other stages of CL (p = 0.007). StAR mRNA expression was minimal in unstimulated ovaries, was higher in preovulatory follicles (p = 0.014), and then rose again in CL (p = 0.009 compared with unstimulated ovary). P450scc mRNA concentrations were low in unstimulated ovaries, increased in preovulatory follicles (p = 0.044), and increased further in CL (p = 0.001 compared with preovulatory follicles). P450scc and StAR mRNA levels correlated with progesterone levels (r = +0.37, p = 0.025, and r = +0.71, p < 0.001, respectively). The expression of LDL receptor, StAR, and P450scc messages showed a dramatic decline by Day 20 post-hCG (p = 0.002, p = 0.003, p = 0.006, respectively, compared with CL) corresponding with functional regression of the CL. In summary, P450scc and StAR message expression are coordinately amplified during the pig follicular and luteal phase, whereas LDL receptor message after an initial increase is expressed at constitutively high levels, thus indicating a differential regulation of ovarian sterol-metabolizing genes during the steroidogenic life of the follicle and CL.

Relaxin and progesterone secretion by aging corpora lutea (days 90-120) was examined in pregnant and lactating gilts compared with that in hysterectomized animals. The length of pregnancy is about 115 days in pigs. Unmated gilts were hysterectomized on day 6 (estrus = day 0). From days 90-101, relaxin concentrations in peripheral plasma remained consistently low in pregnant gilts (range, 0.7-1.5 ng/ml) and less (P less than 0.05) than those in hysterectomized animals (range, 0.9-3.5 ng/ml). Relaxin increased abruptly (P less than 0.01) to a peak of 66 ng/ml in pregnant gilts and 37 ng/ml in hysterectomized animals. Relaxin peaked in pregnant animals at 113 +/- 0.7 days (+/- SE) and in hysterectomized gilts at 113 +/- 0.7 days; gestation length averaged 114 +/- 0.8 days. In pregnant gilts, relaxin decreased from a peak of 66 to 11 ng/ml within 1 day and remained low (less than 1.0 ng/ml) in these lactating dams until day 120. In hysterectomized gilts, peak relaxin also decreased abruptly from 37 to 4.2 ng/ml, but remained consistently greater (P less than 0.05) than that in lactating dams. Although there were abrupt shifts in relaxin concentrations within 20 min, there was no evidence for consistent episodic relaxin release between days 112-116. Plasma progesterone concentrations were consistently greater (P less than 0.05) in hysterectomized than in pregnant gilts from days 102-110. Progesterone decreased abruptly in prepartum gilts (days 111-114) from 16 to 1.2 ng/ml and remained low during lactation (0.5 ng/ml). In hysterectomized animals, it decreased abruptly on days 110-113, ranging from 20-12 ng/ml, and remained at this lower level until day 120. These results clearly indicate that a precisely timed peak release of relaxin and coincident decrease in progesterone secretion occur in unmated hysterectomized gilts at the same time as those found a few hours preceding parturition during normal pregnancy. These abrupt shifts in relaxin and progesterone secretion on days 112-113 in both hysterectomized and pregnant gilts may be regulated autonomously from within the ovary or from the central nervous system and pituitary gland.

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