SUBSTANCE-P (SP) AND NEUROKININ-A (NKA) IN DEVELOPING SUBMANDIBULAR GLANDS OF THE RAT

The effect of isoprenaline, carbachol, substance P (SP) and neurokinin A (NKA) on peroxidase and total protein secretion was studied in the developing postnatal submandibular glands of the rat using in vitro me thods. Submandibular glands of 1, 5, 12 and 30 day-old-rats were stimu lated by 10(-5) M isoprenaline and carbachol, and 10(-6) M SP and NKA. The stimulatory effects of these compounds were compared to the basic release of peroxidase and total amount of protein from submandibular gland fragments in incubation solution with no added transmitter subst ances. Indirect immunohistochemical methods were used to study these d eveloping glands from SP- and NKA-immunoreactive (IR) nerve fibers. Th e distributions of SP-IR and NKA-IR nerve fibers closely resembled eac h other, being most abundantly spread around the developing acini and ducts. The number of these fibers was high on the 1st, 5th and 12th da ys, but was decreased on the 30th day. On peroxidase release, isoprena line was the most effective, causing a maximal response of 47 times th e basic release on the first postnatal day, after which it gradually d ecreased. The effects of carbachol, SP and NKA on peroxidase release w ere clearly weaker and, unlike isoprenaline, their strongest response was on the 5th postnatal day (carbachol, 4.3; SP 5.2; NKA, 4.5). The t otal protein secretion effect patterns of the studied substances resem bled each other more, showing their strongest response on the 5th day (isoprenaline, 5.0; carbachol, 4.5; SP, 4.2; NKA, 3.4) and decreasing thereafter. In general, both the stimulatory pattern of SP and NKA, an d the appearance and distribution of SP-IR and NKA-IR nerve fibers dur ing the early postnatal period of development closely resemble those o f parasympathetic nerves and their transmitters. Furthermore, it is co ncluded that the abundancy of SP-IR and NKA-IR nerves in the developin g submandibular gland is accompanied by the increased sensitivity of t he secretory elements to these tachykinins, indicating that they play a role in the maturation of the glandular secretory functions.