Postnatal DNA-syntheses and mitoses in hearts of dwarf pigs

Postnatal DNA synthesis and mitoses have been investigated in the heart muscle of 23 dwarf pigs by autoradiography and by light and electron microscopy. During the first weeks the average labelling indices of the myocardium decrease from 3.7 +/- 1.6% to 1.9 +/- 0.6%, while considerable individual variations are observed. The average mitotic indices decrease from 1.0 +/- 0.7% on the tenth to 0.2 +/- 0.1% on the 30th day. The number of two synchronous mitotic figures in the same cell increases from 7.5 to 32.5% in the first postnatal month and causes the mitotic development of nuclear rows. The period between 2 and 8 months after birth is characterized by low DNA synthesis at least in one of the investigated ventricular tissues.