Luteal Tissue Area Research Articles

Extended function of the corpus luteum and earlier development of the second follicular wave in heifers treated with bovine somatotropin

Effects of recombinant bovine somatotropin (bST) on growth of the corpus luteum (CL) and development of ovarian follicles were tested. Starting at estrus (Day=0), the following treatments were administered: control (saline injected Days 0 to 19, n=5); bST[0–9] (25 mg bST injected Days 0 to 9, saline injected Days 10 to 19, n=5); bST[10–19] (saline injected Days 0 to 9, 25 mg bST injected Days 10 to 19, n=5); and bST[0–19] (25 mg bST injected Days 0 to 19, n=6). Blood was collected daily for progesterone analysis, and ultrasound examinations were performed daily for measurement of follicles and CL. Compared with the heifers treated with saline, those treated with bST had larger CL and more progesterone during the early (≤ Day 10) and late (Days 15 to 21) phases of the estrous cycle. At mid-cycle (Days 10 to 15), luteal tissue area and progesterone levels were similar for bST- and saline-treated heifers. Ovarian follicular growth was similar for bST- and saline-treated heifers during the first follicular wave. However, during recruitment for the second follicular wave (Days 10 to 14), second largest follicles emerged sooner (P<0.001), the number of Class-3 (≥10 mm) follicles was greater (P<0.01) and largest follicles were smaller (P<0.001) in bST than in saline-treated heifers. Estrous cycle length and ovulation rate were similar for each group. In conclusion, bST increased initial development of the CL and extended its function. Furthermore, the second follicular wave was earlier with bST.

Ultrasonic morphology of corpora lutea and central luteal cavities during the estrous cycle and early pregnancy in heifers

Ultrasonography was used once daily to quantify corpora lutea, central luteal cavities, and luteinized tissue during interovulatory intervals (n = 66) and during Days 0 to 60 of pregnancy (n = 14) in nulliparous Holstein heifers (ovulation = Day 0). The corpus luteum of the estrous cycle was detectable by ultrasonography in most heifers from the day of ovulation (mean, Day 0.5) and extending into the regressive phase beyond the next ovulation (mean, Day 1.4 ±0.2 after the next ovulation). During pregnancy, the corpus luteum was detected until Day 60 (end of study). Maximal central luteal cavity area detected on Days 0 to 20 was used retrospectively to group luteal glands into four cavity categories: no, small, medium, and large. These categories corresponded to approximate cavity diameters of <2 mm, 2 to 5 mm, 6 to 10 mm, and >10 mm, respectively. The incidence of each cavity category was similar between interovulatory intervals and pregnancies (combined incidence, 17 80 , 8 80 , 33 80 , and 22 80 for no, small, medium, and large cavities, respectively; total with cavities, 63 80 , 79%). Mean day of first detection of a central cavity was earliest for large cavities during interovulatory intervals (means, Days 4.7, 4.4, and 3.0 for small, medium, and large cavities, respectively; P<0.04) and during pregnancies (means, Days 5.5, 4.2, and 3.3, respectively; NS). However, the day that the cavities reached maximum size (range of means, Days 5.5 to 7.0) did not differ among categories. Mean day of last detection of the central cavity was significantly different among cavity categories during interovulatory intervals (means, Days 9.3, 11.1, and 17.4 for small, medium, and large cavities, respectively) and pregnancies (means, Days 7.0, 8.8, and 20.2, respectively). Time of loss of central cavities was similar between nonbred and pregnant heifers, and there was no significant difference among cavity categories in the length of the interovulatory interval (mean, 20.1 d). Luteal tissue area was not significantly different among cavity categories during interovulatory intervals. There were no indications that cavities were functionally important. Luteal tissue area increased linearly in pregnant heifers on Days 21 to 60 (mean slope, 2.6 mm 2/day).

Relationship between ultrasonic assessment of the corpus luteum and plasma progesterone concentration in heifers

In nulliparous Holstein heifers, ultrasonography was used to measure cross-sectional areas of corpora lutea, central luteal cavities and luteal tissue on Days 2, 5, 8, and 11 and daily on Days 14 to 21 (pregnant heifers, n = 7) or Day 14 to the day of the subsequent ovulation (nonbred and bred nonpregnant heifers, n = 7 and n = 8, respectively). A blood sample for progesterone assay was collected prior to each ultrasound examination. Combined for the three reproductive statuses, luteal tissue area and plasma progesterone concentration increased (P < 0.0001) over Days 2, 5, 8, and 11; the rate of increase was not significantly different between the two endpoints (12 and 13% of the maximum/day, respectively). There were significant main effects of day and interactions of day by reproductive status for luteal tissue area and for plasma progesterone concentration over Days 14 to 20; luteal tissue area and plasma progesterone concentration were first significantly lower on Days 19 and 17, respectively, in nonbred and nonpregnant heifers than in pregnant heifers. Combined for nonbred and nonpregnant heifers, both luteal tissue area and plasma progesterone concentration first decreased significantly between Days -6 and -4 relative to the second ovulation. Luteal tissue area decreased slower (P < 0.01) than plasma progesterone concentration (mean rates combined for nonbred and nonpregnant heifers, -20 and -28% of the maximum/day, respectively). The correlation coefficients combined for all reproductive statuses were 0.76 and 0.72 during Days 2 to 11 and following Day 14, respectively. The presence and size of central luteal cavities did not affect luteal tissue area or plasma progesterone concentration. Results indicated that ultrasonic assessment of the corpus luteum is a viable alternative to the determination of peripheral progesterone levels for assessment of luteal function in nulliparous Holstein heifers.

Vascular changes during regression of the corpus luteum of the guinea pig.

Quantitative and qualitative changes in the microvasculature of the corpus luteum of the guinea pig during cyclical luteal regression were studied by light and electron microscopy. During luteal regression, between day 12 of the oestrous cycle and day 1 of the next cycle, there was a reduction in the extent of the luteal capillary bed as measured both by 'hit' counts and by differential counts of all nucleated cells. Luteal cells made up a constant proportion of congruent to 60% of the luteal tissue area up to day 1 of the next cycle, but had increased as a proportion of all nucleated cells by that stage. Both fibroblasts and macrophages increased in number and in area occupied during luteal regression. Ultrastructural changes in capillaries during luteal regression included an increased incidence and degree of protrusion of endothelial cells into the lumina of small blood vessels, and degeneration and death of many endothelial cells. In spite of the widespread presence of endothelial cell degeneration, most small vessels retained a continuous lining of apparently viable endothelium. It is concluded that in this species there is a rapid and substantial reduction in the luteal capillary bed, which commences during the early stages of luteal regression, and a mechanism is proposed by which the capillary bed may be reduced while retaining its integrity.