Growth of the cartilages of the mid-line cranial base: a radiographic and histological study.

The importance of controlling litter size in growth studies is verified for Rattus norvegicus. A method of studying growth of the cranial base bones in the median sagittal plane is described and figures for growth rate in micrometres per day have been produced for the age range 4-480 days. The age range 4 to 80 days is identified as the period when 50% of growth takes place and therefore as a period which is particularly useful for growth studies. The presence of a caudorostral gradient in growth rate is suggested by the results. The nomenclature of the cell zones in endochondral growth sites is reviewed and the use of the term matrixogenic is offered to describe and identify more accurately one of the functional zones in endochondral growth sites.

Growth of the cartilages of the mid-line cranial base: an autoradiographic study using tritium labelled thymidine.

Proliferative and kinetic activity of chondrocytes in five sites of endochondral growth in the mid-line cranial base of the rat have been studied using a single injection of 3H-thymidine in animals aged 4-80 days. The marked caudorostral gradient and temporal gradient of the labelling index and labelling profiles is indicative of a proliferative activity specific to each endochondral growth site. Measurements of the growth rate indicate that each growth site in the cranial base bones has a specific growth rate.

Growth of the cartilages of the mid-line cranial base of the Wistar rat: an autoradiographic study using 35S-sulphate.

Matrix synthesis in the mid-line cranial base of the rat was studied using a single injection of 35S-sulphate in animals aged 4-80 days. High uptake of 35S-sulphate in the morphologically distinct zone of early hypertrophy led to it being renamed the Matrixogenic Zone. Relocation of 35S-sulphate label into the primary spongiosa was used to estimate the growth rate of each site of endochondral ossification. This showed a marked caudorostral and temporal gradient. In addition, there was a caudorostral and temporal gradient in hypertrophic cell size, but only a temporal gradient in the rate of cell loss.

Insulin deficiency and cell proliferation in oral mucosal epithelium of the rat.

The duration of the cell cycle (C) and its component phases (G1, S, G2 and M), the rate of cell proliferation, and the renewal time, in the epithelium of the hard palate of alloxan-diabetic rats have been determined and compared with values of the same variables obtained previously from normal rats. The data have been derived by means of autoradiography with [3H]thymidine and the method of labelled mitoses. The values for the normal animals were found to be: G1 = 38 hours, S = 8 hours, G2 = 1 hour, M = 1 hour, C = 48 hours (or 2.1%/hour); and for the diabetic animals were: G1 = 42.5 hours, S = 8.5 hours, G2 = 1 hour, M = 1 hour, C = 53 hours (or 1.9%/hour); and for the renewal time for the epithelium, 6.5-8 days. In the diabetic animals the duration of S was increased by 6%, G1 by 12% and the cell cycle by about 10%. The reduced rate of cell proliferation that is associated with insulin deficiency may contribute to the slower rate of wound healing in subjects with diabetes mellitus.