Growth changes in the craniofacial complex of the rat after prolonged papain administration

Abstract

The purpose of the study was to evaluate by radiographic and biometric means the effects of prolonged papain administration on growth of the craniofacial complex, to gain further insight into the importance of cranial cartilage for skull enlargement during rapid skeletal growth (25 to 70 days of age). Fifty 21-day-old male Lewis strain rats were divided randomly into three groups. Group 1 ( n = 20) received 45 daily injections intraperitoneally of a 2% solution of crude papain in normal saline from 25 to 70 days of age. Group 2 ( n = 20) were given 30 daily injections at the same dose level from 40 to 70 days of age, and group 3 ( n = 10) served as untreated controls. Animals were weighed daily until 70 days of age and then every other day until killed at day 120. Submental-vertex and lateral skull radiographs were obtained at 25, 40, 53, 70, 90, and 120 days of age with standardized skull positioning and radiographic settings. Cephalometric measurements of 22 linear dimensions were made in each of 360 cephalograms, and the data analyzed statistically with Student's t test. Growth velocity curves were evaluated for evidence of catch-up growth. Body-weight gain by papain-treated groups was less than for controls (p < 0.001). Skull and nasal lengths, middle cranial base length, and sphenoidal length were significantly shorter (p < 0.001). Neurocranial length was also shortened, whereas neurocranial height and supraoccipital height increased. Reduction of skull dimensions was generally more pronounced in the earlier injected group. The effectiveness of catch-up growth was not constant and was more successful in the later injected group. Catch-up growth was effective for posterior nasal, neurocranial and supraoccipital heights, cranial width, and posterior cranial base length. The incomplete nature of catch-up growth may have been due to the particular timing and severity of the insult, the frequency of administration of the enzyme and the peak velocity of dimensional growth relative to the time of papain administration. (A M J O RTHOD D ENTOFAC O RTHOP 1994;105:270-8.)