Cyclical changes in collagen concentration in relation to growth and development of buffalo corpus luteum

In the present study, changes in luteal fresh weight and concentration of collagen in cyclic buffalo corpus luteum were investigated at 4 stages of its growth and development/regression. The collagen concentration was determined by estimating hydroxyproline, a collagen specific amino acid present in luteal tissues. The mean fresh weight increased (P < 0.001) over the luteal phase, reached maximum at late-luteal stage and decreased (P < 0.001) subsequently at follicular stage. The weight of the mature CL was 2.5 times heavier than the CL haemorrhagicum and regressing CL. Results showed that cyclic buffalo CL contains collagen at all 4 stages of development during oestrous cycle. The collagen in luteal tissues constitutes about 0.9% to 1.2% of luteal fresh weight with the highest content appearing in mature tissue. The concentration of collagen increased (P < 0.001) with the stages of CL development over the luteal phase and the highest concentration was recorded at follicular phase with the decline of luteal weight. The total content of collagen per CL also showed the same trend during luteal phase but decreased at follicular phase with the loss of luteal tissues. In conclusion, collagen concentration in cyclic buffalo CL changes with the growth and development of CL across the oestrous cycle. The synthesis of collagen is faster between early- to mid-luteal stage than mid- to late-luteal stage.