The Active Neurohypophysial Principles of Two Primitive Bony Fishes, the Bichir (Polypterus Senegalis) and the African Lungfish (Protopterus Aethiopicus)

Abstract

SUMMARY Active neurohypophysial principles were separated from pituitary glands from a primitive actinopterygian, Polypterus senegalis, and the African lungfish, Protopterus aethiopicus. Both species appeared to possess arginine vasotocin (8-arginine oxytocin) and a more nearly neutral principle resembling oxytocin. In the case of Polypterus the neutral principle was pharmacologically indistinguishable from isotocin (4-serine, 8-isoleucine oxytocin). When subjected to partition chromatography on a Sephadex column the neutral Polypterus principle appeared homogeneous and emerged at an elution volume identical with that of isotocin. The neutral principle from Protopterus neurohypophysial extracts resembled mesotocin (8-isoleucine oxytocin) pharmacologically. On partition chromatography it appeared to be a single peptide with mobility comparable to that of mesotocin. No evidence was found for the presence of oxytocin despite earlier reports that this principle occurs in Protopterus and in the South American lungfish, Lepidosiren. From these studies it appears that Polypterus has neurohypophysial principles (arginine vasotocin and isotocin) identical with those found among higher actinopterygians, the Holostei and Teleostei. On the other hand, Protopterus principles resemble those found among Amphibia (arginine vasotocin, mesotocin, and possibly oxytocin).

4-Threonine Analogues of Neurohypophysial Hormones With Selectively Enhanced Oxytocin-Like Activities

“…The activity appeared to vary from assays on one uterus to those on another. Similar variation has been noted previously when an analogue other than oxytocin has been assayed repeatedly against an oxytocin-containing standard (Sawyer, 1969). Thus it is not possible to combine the results of individual assays in the usual manner to achieve an accurate indication of absolute oxytocic activity.…”

“…All the known neurohypophysial peptides in the fishes most nearly related to ancestral mammals, the lungfishes, and in amphibians, reptiles, and birds, contain glutamine in the 4-position (Sawyer, 1968(Sawyer, , 1969. The substitution of threonine for glutamine requires a minimum of two point mutations, the intermediate amino acid being either proline or lysine.…”