PROSTAGLANDINS LEUKOTRIENES AND ESSENTIAL FATTY ACIDS Prostaglandins Leukolrienesand Essential Fatty Acids (1995) 52, 235-239 © Pearson ProfessionalLtd 1995 Prostaglandin Metabolism During Growth and Differentiation of the Regenerating Vertebrate Appendage A. Jayadeep l, P. Reddanna 2, S. Sailesh 2, U. N. Das 3, G. Ramesh 3, K. Vijay Kumar 3 and V. P. Menon 1 1Department of Biochemistry, University of Kerala, Trivandrum 695 581, India. 2School of Life Sciences, University of Hyderabad, Hyderabad 500 134, India. 3Department of Medicine, The Nizam' s Institute of Medical Sciences, Punjagutta, Hyderabad 500 482, India (Reprint requests to VPM) ABSTRACT. House lizards are able to regenerate their tails. This is an ideal model to study the growth and differentiation of an organ. Prostaglandins (PGs) are local hormones having diverse and potent biological activities. In an effort to understand PG metabolism during the growth and differentiation of the regenerating lizard tail, we analysed the fatty acid (FA) composition of phospholipids are free FAs by GC, the activity of two rate-limiting enzymes (phospholipases A and C), the activity of the enzyme responsible for the oxygenation of polyunsaturated fatty acids to PGs (cyclooxygenase) and characterized the endogenous PGs by HPLC. It was observed that on the 20th day, i.e. the tissue differentiation period, there was an increase in phospholipase A activity, together with a sudden fall in the free arachidonic acid (AA) level, an increase in cyclooxygenase activity and the appearance of endogenous PGE 2. PGE 2 can stimulate cyclic adenosine monophosphate (cAMP) production and it may stimulate a cascade of events associated with tissue differentiation. INTRODUCTION Most vertebrates can only repair tissues such as epithelia, bone and liver. But reptiles like the house lizard can repair a lost appendage, the tail. The histological se- quence of events characterizing the process of regenera- tion is essentially the same for all morphologically complex vertebrate appendages. A blastema formed by the accumulation of undifferentiated cells subsequently undergoes proliferation and later differentiates into cell types characteristic of the appendage being formed. This is followed by tissue differentiation associated with the synthesis of tissue-specific substances. All this occurs in a temporally and spatially coordinated sequence, culminating ultimately in the cessation of growth once complete regeneration has been achieved. Prostaglandins (PGs) are oxygenated derivatives of arachidonic acid (AA) (20:4 n 6) or similar polyunsatu- rated fatty acids. Eicosanoids differ from one another in chemical structure, tissue specific biosynthesis and bio- logical activities (1). The interest in PGs centres around the fact that many of them have diverse and potent biological activities (2). Not much work has so far been carried out on the role of PGs in the growth and differentiation of an organ. But Date received 13 August 1993 Date accepted 7 February 1994 235 there are a few reports on the involvement of PGs during differentiation. Chepenik et al (3) reported the involve- ment of PGE 2 and PGI 2 during the differentiation of chick limb mesenchymal cells in vitro. Kosher and Walker (4) demonstrated that PGE 2 elicits stimulation of limb carti- lage differentiation in organ culture. Biddulph et al (5) also demonstrated the role of PGE2 during cartilage differentiation of chick limb mesenchyme in vitro. The reports suggest the involvement of PGs during differentiation. But there is no report on PG metabolism in vivo during embryonic development or regeneration of a vertebrate appendage. In the absence of such investigations we thought it worthwhile to study PG metabolism during the growth and differentiation of regenerating lizard tail. MATERIALS AND METHODS Experimental protocol The animal for this study was the house lizard, Hemidactylus frenatus. The tail was amputated by pinching with forceps at around 1.5 cm from the vent and then allowed to regenerate for 65 days. The appear- ance of an appreciable amount of tail bud occurs by around 15 days after amputation. The regenerating part of the tail tissue was sampled 15, 20, 25, 35 and 65 days after amputation. Normal (N) tail was also sampled.