Accessory corpus luteum regression during pregnancy I: timing, physiology, and P4 profiles.

Inappropriate corpus luteum (CL) regression can produce pregnancy loss. An experimental model was utilized to investigate regression of accessory CL during pregnancy in dairy cows. Cows were bred (day 0) and treated with gonadotrophin-releasing hormone 6 days later to form accessory CL. Transrectal ultrasound (every other days) and blood samples for progesterone (P4; daily) were performed until day 56 of pregnancy. On day 28, 13 cows were confirmed pregnant, and accessory CL were found contralateral (n = 9) or ipsilateral (n = 4) to previous ovulation. On day 18, CL biopsy was performed to analyze mRNA expression for interferon-stimulated genes (ISGs). Luteolysis occurred more frequently in cows that had contralateral accessory CL (88.9% (8/9)) than in cows with ipsilateral accessory CL (0% (0/4)). Luteolysis of contralateral accessory CL occurred either earlier (days 19-23; 2/8) or later (days 48-53; 6/8) in pregnancy and occurred rapidly (24 h), based on daily P4. After onset of earlier or later accessory CL regression, circulating P4 decreased by 41.2%. There was no difference in luteal tissue mRNA expression for ISGs on day 18 between accessory and original CL and between CL that subsequently regressed or did not regress. On day 56, an oxytocin challenge dramatically increased prostaglandin F2α metabolite (PGFM) in all cows but produced no pregnancy losses, although cows with previous accessory CL regression had greater PGFM. In summary, ipsilateral accessory CL did not regress during pregnancy, whereas most contralateral CL regressed by 63 days of pregnancy, providing evidence for local mechanisms in regression of accessory CL and protection of CL during pregnancy.

Interactions of circulating estradiol and progesterone on changes in endometrial area and pituitary responsiveness to GnRH†.

Changes in circulating progesterone (P4) and estradiol (E2) during proestrus produce dynamic changes in endometrial function and pituitary release of gonadotropins. Independent and combined effects of P4 and E2 on endometrium and pituitary were evaluated. In a preliminary study, an exogenous hormone model of proestrus was created by removal of corpus luteum and follicles ≥5 mm followed by gradual removal of intravaginal P4 implants during 18 h and treatment with increasing doses of estradiol benzoate during 48 h to mimic proestrus using high E2 (n = 9) or low E2 (n = 9). Decreased P4, increased E2, and increased endometrial area (EA) simulated proestrus in high-E2 cows and this was used subsequently. The main experiment used a 2 × 2 factorial design with: high E2 and low P4 (n = 11); high E2 and high P4 (n = 11); low E2 and high P4 (n = 11); low E2 and low P4 (n = 10). At 48 h, gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) and follicle stimulating hormone (FSH) release was determined. Variables were analyzed using PROCMIXED of Statistical Analysis System. The EA increased dramatically during 48 h only in high-E2 and low-P4 cows. For FSH, high-E2 cows had greater area under the curve (AUC) and FSH peak after GnRH than low E2, with mild negative effects of high P4. For LH, concentration at peak and AUC were 2-fold greater in high E2 compared to low-E2 groups, with low P4 also 2-fold greater than high-P4 groups. Thus, maximal changes in uterus and pituitary during proestrus depend on both low P4 and high E2, but different physiologic responses are regulated differently by E2 and P4. Changes in endometrium depend on low P4 and high E2, whereas GnRH-induced FSH secretion primarily depends on high E2, and GnRH-induced LH secretion is independently increased by high E2 or reduced by high P4.

Continuous infusion of propofol in calves: bispectral index and hemodynamic effects.

OBJECTIVE: To assess the bispectral index (BIS) and the hemodynamic effects of propofol administered by continuous infusion at different rates in calves. STUDY DESIGN: Experimental crossover study. ANIMALS: Eight intact male Dutch calves, aged 6-12 months and weighing 84-124 kg. METHODS: The calves were anesthetized with propofol (5 mg kg(-1) ) intravenously (IV), and after endotracheal intubation, positioned in right lateral recumbency and allowed to breathe ambient air. Anesthesia was maintained by continuous infusion of propofol, administered IV with an infusion pump at 0.6 mg kg(-1)  minute(-1) (treatment G6) or 0.8 mg kg(-1)  minute(-1) IV (treatment G8), for 60 minutes. The eight animals were anesthetized twice, 1 week apart. The following hemodynamic variables and BIS were assessed before the induction of anesthesia (baseline) and 15, 30, 45, and 60 minutes after beginning the infusion of propofol: heart rate, systolic, diastolic and mean arterial pressures, cardiac output, mean pulmonary artery pressure, cardiac index, stroke index, pulmonary vascular resistance index, and systemic vascular resistance index, BIS, electromyography, and signal quality index. RESULTS: The continuous infusions of propofol at different rates did not alter BIS variables during the infusion time between dose rates, and no clinically significant hemodynamic changes were observed. CONCLUSIONS AND CLINICAL RELEVANCE: A continuous infusion of propofol at 0.6 or 0.8 mg kg(-1)  minute(-1) caused minimal hemodynamic changes without clinical relevance in calves. BIS could not be reliably used to discriminate the anesthetic depth during the two propofol infusion rates.