Allometric analysis of the postnatal growth of rat submandibular gland

ABSTRACT

The rat submandibular gland grows significantly during the first 10 weeks of postnatal life. During this growth, there is differentiation and maturation of the definitive glandular structures, (acini, intercalated ducts, convoluted granular tubules, striated ducts and excretory ducts) within a highly vascularized stroma. In this study, the absolute volume of each glandular component during postnatal development was determined morphometrically. The increases in gland mass and component volumes were analyzed allometrically relative to the growth of body mass, using Wald’s non-parametric method. The allometric growth of gland mass was monophasic and negative (k<1), with k = 0.86. The absolute volumes of the acini plus terminal tubules, intercalated ducts, striated ducts and excretory ducts all showed a biphasic pattern, with the first phase occuring from day 2 to day 28 and the second phase from day 28 to day 96. In the first phase, all of the structures showed positive allometric growth (k>1), with k values from 1.09, 1.15, 1.49 and 1.17, for the acini plus terminal tubules, intercalated ducts, striated ducts and excretory ducts, respectively, while in the second phase, all showed negative allometrtic growth (k<1), with k values of 0.72, 0.33, 0.77 and 0.82, respectively. The convoluted granular tubules showed a single phase of positive allometric growth (k>1) between 28 and 96 days of age, with k=1.28, whereas the stromal volume showed negative allometric growth (k<1) from day 14 to day 96, with k=0.77.