Differential processing of Asn-linked oligosaccharides on pituitary glycoprotein hormones: implications for biologic function

Luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone from pituitary and chorionic gonadotropin from placenta are a family of glycoproteins, each consisting of an and subunit. Within an animal species, the subunit of all four hormones contains the identical amino acid sequence, while each subunit is distinct and confers biologic specificity to the hormone dimer. Despite sharing common subunits, these hormones bear Asn-linked oligosaccharides which differ in structure. Whereas chorionic gonadotropin contains exclusively neutral and sialylated oligosaccharides, the pituitary hormones bear neutral, sialylated, sulfated, and sialylated/sulfated structures. The sulfated oligosaccharides are unique in structure and are more prevalent on certain pituitary hormones, indicating that the synthesis of these unusual oligosaccharides is tightly regulated. The differences in oligosaccharide structures in conjunction with the highly specific endocrine responses elicited by these hormones, suggest an important functional role for the oligosaccharides, such as metabolic clearance, control of hormone response, modulation of hormone potency, and/or intracellular sorting of hormones into separate secretory granules.     

Differential subcellular localization of ACTH and α-MSH in corticotropes of the rat anterior pituitary

Summary Specific antisera to -melanotropin (-MSH) and corticotropin (ACTH 1-39) were used to obtain immunocytochemical evidence for the differential localization of -MSH and ACTH in the secretory granules of corticotropes of rat anterior pituitary. The specificity of the antisera was established by binding ¹³¹I-labeled -MSH and ACTH 1-39 to their respective antisera. Double-labeling immunocytochemistry (for -MSH, ferritin; for ACTH, colloidal gold) was performed. Some secretory granules were labeled with ferritin particles (-MSH), whereas others contained gold particles (ACTH). Only a few granules showed both ACTH and -MSH. In typical corticotropes (stellate in form with a small number of secretory granules aligned along the cell periphery) only some of the secretory granules that were labeled with anti-ACTH serum were also immunoreactive to anti--MSH. In atypical corticotropes (polygonal in shape and containing a large number of secretory granules) almost all of the immunoreactive ACTH secretory granules were also positive to anti--MSH serum. An intermediate type of corticotrope was observed containing a small number of secretory granules, almost all of which were labeled with anti--MSH. Thus, rat anterior pituitary corticotropes may be classified into three types according to the distribution and content of -MSH. The light-microscopic immuncytochemistry provided similar results.     

A possible phagocytic role for folliculo-stellate cells of anterior pituitary following estrogen withdrawal from primed male rats

Summary Ultrastructural changes suggesting a phagocytic role for the nongranular folliculo-stellate cells of the anterior pituitary are investigated in estrogen-primed male rats after withdrawal of estrogen. Morphological changes in mammotropes following the removal of a subcutaneous estradiol-containing Silastic implant include the formation of intracellular lipid bodies. These lipid bodies appear to be associated with enhanced estrogen-dependent prolactin secretion in mammotropes. Seven and 24 h after estrogen withdrawal intracellular lipid within mammotropes seems to be released into the intercellular space. Seventy-two h after estrogen withdrawal, lipid droplets are almost entirely cleared from mammotropes while folliculo-stellate cells become packed with lipid globules. Folliculo-stellate cells also undergo dramatic hypertrophy 7 and 24 h after the removal of E2-containing implants. Extensive intercellular junctions including zonulae adhaerentes, desmosomes, and putative gap junctions are formed. Intercellular junctions delineate extravascular channels into which numerous microvilli project. Folliculo-stellate cells appear capable of accumulating many lipid droplets, presumably related to mammotrope metabolism. What appear to be large secondary lysosomes as well as the lipid droplets are observed within folliculostellate cells; lipid, therefore, may be degraded through a lysosomal pathway in folliculo-stellate cells.     

Biosynthesis and distribution of ecdysone and 20-OH-ecdysone in Aedes aegypti

The distribution and biosynthesis of ecdysone and 20-hydroxyecdysone (20-OH-ecdysone) was followed in sugar- and blood-fed female Aedes aegypti. In both sugar- and early blood-fed animals most of the ecdysteroid determined by radioimmunoassay was found outside the ovary. Twenty-four to 40 h after blood feeding, however, ecdysteroid was distributed between ovary and carcass in the ratio of 1:1.5. Ecdysteroid titer reached a plateau between 18 to 40 h after the blood meal and decreased thereafter. Analysis of the ecdysteroid titer using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) revealed that both 20-OH-ecdysone and ecdysone were synthesized after the blood meal. The ratio of 20-OH-ecdysone to ecdysone remained essentially constant and fluctuated in parallel throughout egg development. Chromatography of the early ecdysteroid peak (8 h after feeding) using TLC and HPLC indicated that although it cross-reacted with ecdysteroid antibodies, it did not have the same elution times as ecdysone and 20-OH-ecdysone and is, therefore, probably a precursor of these ecdysteroids. Injections of egg development neurosecretory hormone (EDNH) preparation purified to near homogeneity, into ligated abdomens, induced ecdysteroid synthesis only if the abdomens were first treated with methoprene (12.5 pg). Methoprene at this concentration did not stimulate ecdysteroid synthesis in these abdomens. When blood-fed females were treated with [4-¹⁴C] cholesterol and analyzed using TLC and HPLC procedures, both [¹⁴C]labeled ecdysone and [¹⁴C]labeled 20-OH-ecdysone were synthesized in the ratio of 1:1.5. This report is the first to show that both ecdysone and 20-OH-ecdysone are synthesized in vivo in female A. aegypti.     

Disinhibition of oocyte growth in adult,virgin Periplaneta americana by corpus allatum denervation: Age dependency and relatedness to mating

Unilateral section of the nervi corporis allati I (NCA-1) of isolated, starved, adult, virgin Periplaneta americana disinhibited oocyte growth during a specific period following their adult emergence. The effect required that the corpus allatum (CA) be free of NCA-1 innervation for 4 days beyond the time the females were 7–8 days old. The onset of this sensitive period corresponds to when most isolated, starved virgins become sexually receptive. The results suggest that NCA-1 inhibition of CA activity, initiated about 7 days, is relieved by mating. When done on sexually receptive, starved virgins, unilateral NCA-1 section was as effective as insemination for stimulating growth and chorionation of the first generation of oocytes. Neural inhibition of juvenile hormone (JH) secretion by the CA may also explain diminished production of oocytes by isolated, fed virgins, for during 30 days following unilateral NCA-1 section they produced 2.6 to 5 times more oothecae than did controls with a single CA removed or after the sham operation. The number of oothecae deposited by fed virgins was similarly increased after bilateral NCA-1 section, but to a lesser extent than when the operation was done on fed, inseminated females of the same age. Specificity of the response of the CA to denervation was substantiated by experiments in which the CA were extirpated and reimplanted, by topically applying C₁₆JH, and by experiments in which the nervus corporis cardiaci 1 and 2 on the right or left side were severed.     

Liposome-mediated labeling of adrenocorticotropin fragments parallels their biological activity

To test our hypothesis that specific interactions of ACTH peptides with model lipid membranes reflect the biological importance of similar interactions on target cells, we investigated the liposome-mediated labeling of ACTH fragments with the extremely hydrophobic photolabel, 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine. Correlations were found between the labeling rates and the agonistic and antagonistic potencies of the peptides for in vitro steroidogenesis and inhibition of a synaptosomal protein kinase. A model for the cross-reactivity between ACTH and opioid peptides is discussed.     

Philomena oncorhynchi: Effect of hormones on maturation in anadromous sockeye, Oncorhynchus nerka

Adult sockeye salmon, Oncorhynchus nerka (Walbaum), treated with salmon pituitary extract in July survived for up to 47 days and developed nuptial colours in both male and female fish during this period, whereas no such characteristics appeared in untreated control fish. Furthermore, results showed that 20 of 50 adult female Philomena oncorhynchi recovered from the 15 treated fish contained fully developed tailed larvae in the uterus as compared with only one of 44 female P. oncorhynchi from 31 untreated control fish. None of 51 worms from 13 stilboestrol treated adult sockeye showed development in utero beyond an elongated embryo, nor did the host fish develop nuptial colours. P. oncorhynchi and its immature sockeye host (approx. 1 year prior to spawning) remained unaffected by any of three separate hormone treatment experiments using injection of salmon pituitary extract, injection of 17-β-estradiol, and stilboestrol mixed in the food.     

Effects of secretin and gastric inhibitory polypeptide on human pancreatic growth hormone-releasing factor(1-40)-stimulated growth hormone levels in the rat

Synthetic human pancreatic growth hormone-releasing factor containing 40 amino acids ([hpGRF (1-40)]-OH) significantly stimulated plasma growth hormone (GH) levels in both sodium pentobarbital and urethane anesthetized rats. Synthetic secretin, gastric inhibitory polypeptide (GIP), and glucagon significantly decreased plasma GH levels while synthetic vasoactive intestinal peptide (VIP) had no effect. Secretin and GIP also altered the in vivo plasma GH response to [hpGRF(1-40)]-OH. Whether this effect is the result of an interaction at the pituitary level or is due to an extra-pituitary effect of secretin and GIP awaits further study.     

Precocene causes male determination in the aphid Myzus persicae

When adult apterous viviparous females of Myzus persicae, reared in short night conditions at 21–23°C, are treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, they deposit males towards the end of their reproductive lives. The first-born normal daughters of the treated females also deposit some males at various times in their reproductive lives. Karyotypic analysis was used to investigate the sequence of male and female embryos in the ovarioles of precociously metamorphosed aphids. The experiments support the hypothesis (Mittler et al., 1979) that juvenile hormone level controls the sex determination process in aphids. Since male aphids have an XO sex chromosome constitution, this implies that juvenile hormone level influences the behaviour of the X-chromosomes at or before the single maturation division of the egg. At this division one X-chromosome is eliminated from eggs which will develop as males. Aphids provide the first example of a specific endocrine influence on chromosome behaviour in sex determination.     

Effects of decapitation and ovariectomy on the regulation of juvenile hormone synthesis in the cockroach, Diploptera punctata

Corpora allata from Diploptera punctata females at adult ecdysis or at the end of the last-larval stadium, when implanted into decapitated females, underwent a cycle of juvenile hormone synthesis similar in timing and magnitude to that of glands implanted into control animals which had been starved and allatectomized. Starvation did not alter the cycle in rates of juvenile hormone synthesis of sham-operated animals.Decapitation of ovariectomized animals resulted in no cycle in rates of juvenile hormone synthesis by implanted adult corpora allata; however, implantation of an ovary along with the corpora allata into decapitated, ovariectomized hosts resulted in a cycle of juvenile hormone synthesis. In control animals, which retained their heads but were starved and allatectomized as well as ovariectomized, the implanted corpora allata showed a cycle of juvenile hormone synthesis only when implanted with an ovary. The maximal rates of juvenile hormone synthesis by the corpora allata in both experimental and control conditions were lower than normal, likely due to the repeated trauma of surgery. However, at no time from eclosion to the end of the first gonotrophic period was the brain necessary for the cyclic response of the corpora allata to the presence of the ovary.