In cardiac hypertrophy induced by GH, the turn-over of collagen seems to be increased. Matrix metalloproteinases (MMP) are enzymes suggested to contribute to the remodelling of the extracellular matrix in the myocardium. The aim of the present experiment was to investigate how GH influenced MMP concentration, collagen concentration, and structure of the connective tissue of the LV in young rats in relation to time. Three-month-old female rats were injected with GH (5mg/kg/day) or vehicle for 5, 10, 20, 40, or 80 days. MMPs and structural changes of the connective tissue were analysed using zymography and stereology, respectively. Wet weight of the LV was increased time-dependently by GH (r = 0.89, P < 0.001). Furthermore, GH increased the MMP-2 concentration (P < 0.01, two-way ANOVA), whereas no collagenases (MMP-1, MMP-8, or MMP-13) could be demonstrated. The increase in MMP-2 was accompanied by a time-dependent decrease in the collagen concentration (r = -0.46, P < 0.05), whereas the total collagen content (r = 0.85, P < 0.01) and total number of non-myocyte nuclei (GH: r = 0.89, P < 0.001) were time-dependently increased. These results indicate that MMP-2 may be involved in the remodelling process of the extracellular matrix in GH-induced cardiac hypertrophy.