ULTRASOUND IMAGE ATTRIBUTES OF THE BOVINE CORPUS-LUTEUM - STRUCTURAL AND FUNCTIONAL CORRELATES

Nulliparous heifers (n = 58) were studied to determine whether compute r-assisted quantitative echotexture analysis of ultrasound images refl ects the functional and histomorphological characteristics of the corp us luteum. The ovaries of heifers were examined daily by transrectal u ltrasonography from day - 2 (day 0 = ovulation) until the day of ovari ectomy during metoestrus (day 3; n = 8), early dioestrus (day 6; n = 9 ), mid-dioestrus (mean, day 10; n = 7), or pro-oestrus (mean, day 18; n = 8; Expt I). High resolution ultrasound images of corpora lutea wer e obtained in vitro, and were digitized and analysed using custom-deve loped computer algorithms optimized for ultrasonography. Cryostat sect ions of corpora lutea were examined for lipid distribution, and corpor a lutea were homogenized to determine the content of progesterone, tot al protein, cholesterol and triglyceride. In Expt 2, heifers (n = 26) were ovariectomized as in Expt 1, and ovaries were prepared for histom orphometric evaluation. Pixel values (brightness of picture elements) of ultrasound images of corpora lutea were characterized as high durin g metoestrus, low during early and mid-dioestrus, and increasing again during pro-oestrus (P < 0.05). Changes (P < 0.001) in volume density of luteal cells were characterized as increasing from metoestrus (40.7 +/- 0.4%) to mid-dioestrus (55.8 +/- 2.8%) and decreasing again at pr o-oestrus (41.5 +/- 0.9%). The proportion of blood vascular components decreased (P < 0.001) progressively from 31.0 +/- 1.0% in metoestrus to 15.6 +/- 1.1% in pro-oestrus. Pixel values of ultrasound images of corpora lutea were correlated with luteal (r = -0.72, P < 0.05) and pl asma (r = -0.71, P < 0.03) progesterone concentration, and to the volu me densities of luteal cells (r = -0.75, P < 0.02) and connective tiss ue (r = 0.69, P < 0.03). Estimates of triglyceride, protein and choles terol content of corpora lutea were not correlated with pixel values o f ultrasound images. Protein and cholesterol content did not change wh ile triglyceride concentration increased during pro-oestrus (P < 0.05) . Results support the hypothesis that ultrasound images reflect luteal and plasma progesterone content, and histomorphological characteristi cs of the corpus luteum.